Pairwise fitting of piecewise mixed models for the joint modeling of multivariate longitudinal outcomes, in a randomized crossover trial

Many statistical models have been proposed in the literature for the analysis of longitudinal data. One may propose to model two or more correlated longitudinal processes simultaneously, with a goal of understanding their association over time. Joint modeling is then required to carefully study the association structure among the outcomes as well as drawing joint inferences about the different outcomes. In this study, we sought to model the associations among six nutrition outcomes while circumventing the computational challenge posed by their clustered and high-dimensional nature. We analyzed data from a 2 × $\times$ 2 randomized crossover trial conducted in Kenya, to compare the effect of high-dose and low-dose iodine in household salt on systolic blood pressure (SBP) and diastolic blood pressure (DBP) in women of reproductive age and their household matching pair of school-aged children. Two additional outcomes, namely, urinary iodine concentration (UIC) in women and children were measured repeatedly to monitor the amount of iodine excreted through urine. We extended the model proposed by Mwangi et al. (2021, Communications in Statistics: Case Studies, Data Analysis and Applications, 7(3), 413-431) allowing flexible piecewise joint models for six outcomes to depend on separate random effects, which are themselves correlated. This entailed fitting 15 bivariate general linear mixed models and deriving inference for the joint model using pseudo-likelihood theory. We analyzed the outcomes separately and jointly using piecewise linear mixed-effects (PLME) model and further validated the results using current state-of-the-art Jones and Kenward methodology (JKME model) used for analyzing randomized crossover trials. The results indicate that high-dose iodine in salt significantly reduced blood pressure (BP) compared to low-dose iodine in salt. Estimates for the random effects and residual error components showed that SBP and DBP had strong positive correlation, with effect of the random slope indicating that significantly related outcomes are strongly associated in their evolution. There was a moderately strong inverse relationship between evolutions of UIC and BP both in women and children. These findings confirmed the original hypothesis that high-dose iodine salt has significant lowering effect on BP. We further sought to evaluate the performance of our proposed PLME model against the widely used JKME model, within the multivariate joint modeling framework through a simulation study mimicking a2 × 2 $2\times 2$ crossover design. From our findings, the multivariate joint PLME model performed exceptionally well both in estimation of random-effects matrix (G) and Hessian matrix (H), allowing satisfactory model convergence during estimation. It allowed a more complex fit to the data with both random intercepts and slopes effects compared to the multivariate joint JKME model that allowed for random intercepts only. When a hierarchical viewpoint is adopted, in the sense that outcomes are specified conditionally upon random effects, the variance-covariance matrix of the random effects must be positive definite. In some cases, additional random effects could explain much variability in the data, thus improving precision in estimation of the estimands (effect size) parameters. The key highlight in this evaluation shows that multivariate joint JKME model is a powerful tool especially while fitting mixed models with random intercepts only, in crossover design settings. Addition of random slopes may lead to model complexities in most cases, resulting in unsatisfactory model convergence during estimation. To circumvent convergence pitfalls, extention of JKME model to PLME model allows a more flexible fit to the data (generated from crossover design settings), especially in the multivariate joint modeling framework.

Contrasting principal stratum and hypothetical strategy estimands in multi-period crossover trials with incomplete data

Complete case analyses of complete crossover designs provide an opportunity to make comparisons based on patients who can tolerate all treatments. It is argued that this provides a means of estimating a principal stratum strategy estimand, something which is difficult to do in parallel group trials. While some trial users will consider this a relevant aim, others may be interested in hypothetical strategy estimands, that is, the effect that would be found if all patients completed the trial. Whether these estimands differ importantly is a question of interest to the different users of the trial results. This paper derives the difference between principal stratum strategy and hypothetical strategy estimands, where the former is estimated by a complete-case analysis of the crossover design, and a model for the dropout process is assumed. Complete crossover designs, that is, those where all treatments appear in all sequences, and which compare t treatments over p periods with respect to a continuous outcome are considered. Numerical results are presented for Williams designs with four and six periods. Results from a trial of obstructive sleep apnoea-hypopnoea (TOMADO) are also used for illustration. The results demonstrate that the percentage difference between the estimands is modest, exceeding 5% only when the trial has been severely affected by dropouts or if the within-subject correlation is low.

Solutions for surrogacy validation with longitudinal outcomes for a gene therapy

Valid surrogate endpoints S can be used as a substitute for a true outcome of interest T to measure treatment efficacy in a clinical trial. We propose a causal inference approach to validate a surrogate by incorporating longitudinal measurements of the true outcomes using a mixed modeling approach, and we define models and quantities for validation that may vary across the study period using principal surrogacy criteria. We consider a surrogate-dependent treatment efficacy curve that allows us to validate the surrogate at different time points. We extend these methods to accommodate a delayed-start treatment design where all patients eventually receive the treatment. Not all parameters are identified in the general setting. We apply a Bayesian approach for estimation and inference, utilizing more informative prior distributions for selected parameters. We consider the sensitivity of these prior assumptions as well as assumptions of independence among certain counterfactual quantities conditional on pretreatment covariates to improve identifiability. We examine the frequentist properties (bias of point and variance estimates, credible interval coverage) of a Bayesian imputation method. Our work is motivated by a clinical trial of a gene therapy where the functional outcomes are measured repeatedly throughout the trial.

Sex-specific responses in glucose-insulin homeostasis and lipoprotein-lipid components after high-dose supplementation with marine n-3 PUFAs in abdominal obesity: a randomized double-blind crossover study

Background

Clinical studies on effects of marine-derived omega-3 (n-3) polyunsaturated fatty acids (PUFAs), mainly eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), and the plant-derived omega-6 (n-6) PUFA linoleic acid (LA) on lipoprotein-lipid components and glucose-insulin homeostasis have shown conflicting results, which may partly be explained by differential responses in females and males. However, we have lacked data on sexual dimorphism in the response of cardiometabolic risk markers following increased consumption of n-3 or n-6 PUFAs.

Objective

To explore sex-specific responses after n-3 (EPA + DHA) or n-6 (LA) PUFA supplementation on circulating lipoprotein subfractions, standard lipids, apolipoproteins, fatty acids in red blood cell membranes, and markers of glycemic control/insulin sensitivity among people with abdominal obesity.

Methods

This was a randomized double-blind crossover study with two 7-week intervention periods separated by a 9-week washout phase. Females (n = 16) were supplemented with 3 g/d of EPA + DHA (fish oil) or 15 g/d of LA (safflower oil), while males (n = 23) received a dose of 4 g/d of EPA + DHA or 20 g/d of LA. In fasting blood samples, we measured lipoprotein particle subclasses, standard lipids, apolipoproteins, fatty acid profiles, and markers of glycemic control/insulin sensitivity.

Results

The between-sex difference in relative change scores was significant after n-3 for total high-density lipoproteins (females/males: -11%*/-3.3%, p = 0.036; *: significant within-sex change), high-density lipoprotein particle size (+2.1%*/-0.1%, p = 0.045), and arachidonic acid (-8.3%*/-12%*, p = 0.012), and after n-6 for total (+37%*/+2.1%, p = 0.041) and small very-low-density lipoproteins (+97%*/+14%, p = 0.021), and lipoprotein (a) (-16%*/+0.1%, p = 0.028). Circulating markers of glucose-insulin homeostasis differed significantly after n-3 for glucose (females/males: -2.1%/+3.9%*, p = 0.029), insulin (-31%*/+16%, p < 0.001), insulin C-peptide (-12%*/+13%*, p = 0.001), homeostasis model assessment of insulin resistance index 2 (-12%*/+14%*, p = 0.001) and insulin sensitivity index 2 (+14%*/-12%*, p = 0.001), and quantitative insulin sensitivity check index (+4.9%*/-3.4%*, p < 0.001).

Conclusion

We found sex-specific responses after high-dose n-3 (but not n-6) supplementation in circulating markers of glycemic control/insulin sensitivity, which improved in females but worsened in males. This may partly be related to the sex differences we observed in several components of the lipoprotein-lipid profile following the n-3 intervention.

Clinical trial registration

https://clinicaltrials.gov/, identifier [NCT02647333].

Best (but oft forgotten) practices: Efficient sample sizes for commonly used trial designs

Designing studies such that they have a high level of power to detect an effect or association of interest is an important tool to improve the quality and reproducibility of findings from such studies. Since resources (research subjects, time, and money) are scarce, it is important to obtain sufficient power with minimum use of such resources. For commonly used randomized trials of the treatment effect on a continuous outcome, designs are presented that minimize the number of subjects or the amount of research budget when aiming for a desired power level. This concerns the optimal allocation of subjects to treatments and, in case of nested designs such as cluster-randomized trials and multicenter trials, also the optimal number of centers versus the number of persons per center. Since such optimal designs require knowledge of parameters of the analysis model that are not known in the design stage, in particular outcome variances, maximin designs are presented. These designs guarantee a prespecified power level for plausible ranges of the unknown parameters and minimize research costs for the worst-case values of these parameters. The focus is on a 2-group parallel design, the AB/BA crossover design, and cluster-randomized and multicenter trials with a continuous outcome. How to calculate sample sizes for maximin designs is illustrated for examples from nutrition. Several computer programs that are helpful in calculating sample sizes for optimal and maximin designs are discussed as well as some results on optimal designs for other types of outcomes.

The Effects of Different Modalities of an Acute Energy Deficit on Sleep and Next Morning Appetitive and Compensatory Behavior in Healthy Young Adults: The EDIES Protocol

Sleep is bi-directionally linked to energy balance. This crossover study design will evaluate the acute effect of a moderate energy deficit (500 kcal) induced by diet, exercise, or mixed (-250 kcal by diet and 250 kcal by exercise) on sleep and the next morning's appetitive responses. The study sample comprises 24 healthy young adults. The experimental measurements will be conducted in a naturalistic, momentary manner and partly assessed by the participants. The participants will undergo a run-in period in order to stabilize their sleep schedules and provide them with training on the study protocol and measurements. Indirect calorimetry will be used to determine their resting metabolic rate and peak oxygen consumption (VO₂ peak). Then, they will take part in a control session (CTL), followed by three energy deficit sessions in random order: a diet-induced energy deficit session (DED), an exercise-induced energy deficit session (EED), and a mixed energy deficit session (MED). All experimental sessions will be separated by a one-week washout. The participants' sleep will be monitored by ambulatory polysomnography, and the next morning's appetitive response will be evaluated via ad libitum food intake, appetite sensations, and food reward, measured by a food liking and wanting computerized test.

Utility of a multimodal computer-based assessment format for assessment with a higher degree of reliability and validity

Multiple choice questions (MCQs) suffer from cueing, item quality and factual knowledge testing. This study presents a novel multimodal test containing alternative item types in a computer-based assessment (CBA) format, designated as Proxy-CBA. The Proxy-CBA was compared to a standard MCQ-CBA, regarding validity, reliability, standard error of measurement, and cognitive load, using a quasi-experimental crossover design. Biomedical students were randomized into two groups to sit a 65-item formative exam starting with the MCQ-CBA followed by the Proxy-CBA (group 1, n = 38), or the reverse (group 2, n = 35). Subsequently, a questionnaire on perceived cognitive load was taken, answered by 71 participants. Both CBA formats were analyzed according to parameters of the Classical Test Theory and the Rasch model. Compared to the MCQ-CBA, the Proxy-CBA had lower raw scores (p < 0.001, η² = 0.276), higher reliability estimates (p < 0.001, η² =  0.498), lower SEM estimates (p < 0.001, η² = 0.807), and lower theta ability scores (p < 0.001, η² = 0.288). The questionnaire revealed no significant differences between both CBA tests regarding perceived cognitive load. Compared to the MCQ-CBA, the Proxy-CBA showed increased reliability and a higher degree of validity with similar cognitive load, suggesting its utility as an alternative assessment format.

The effect of modest changes in sleep on dietary intake and eating behavior in children: secondary outcomes of a randomized crossover trial

BACKGROUND

Insufficient sleep duration increases obesity risk in children, but the mechanisms remain unclear.

OBJECTIVES

This study seeks to determine how changes in sleep influence energy intake and eating behavior.

METHODS

Sleep was experimentally manipulated in a randomized, crossover study in 105 children (8-12 y) who met current sleep guidelines (8-11 h/night). Participants went to bed 1 h earlier (sleep extension condition) and 1 h later (sleep restriction condition) than their usual bedtime for 7 consecutive nights, separated by a 1-wk washout. Sleep was measured via waist-worn actigraphy. Dietary intake (2 24-h recalls/wk), eating behaviors (Child Eating Behavior Questionnaire), and the desire to eat different foods (questionnaire) were measured during or at the end of both sleep conditions. The type of food was classified by the level of processing (NOVA) and as core or noncore (typically energy-dense foods) foods. Data were analyzed according to 'intention to treat' and 'per protocol,' an a priori difference in sleep duration between intervention conditions of ≥30 min.

RESULTS

The intention to treat analysis (n = 100) showed a mean difference (95% CI) in daily energy intake of 233 kJ (-42, 509), with significantly more energy from noncore foods (416 kJ; 6.5, 826) during sleep restriction. Differences were magnified in the per-protocol analysis, with differences in daily energy of 361 kJ (20, 702), noncore foods of 504 kJ (25, 984), and ultraprocessed foods of 523 kJ (93, 952). Differences in eating behaviors were also observed, with greater emotional overeating (0.12; 0.01, 0.24) and undereating (0.15; 0.03, 0.27), but not satiety responsiveness (-0.06; -0.17, 0.04) with sleep restriction.

CONCLUSIONS

Mild sleep deprivation may play a role in pediatric obesity by increasing caloric intake, particularly from noncore and ultraprocessed foods. Eating in response to emotions rather than perceived hunger may partly explain why children engage in unhealthy dietary behaviors when tired. This trial was registered at Australian New Zealand Clinical Trials Registry; ANZCTR as CTRN12618001671257.

Urinary Sodium Excretion and Salt Intake Are Not Associated With Blood Pressure Variability in a White General Population

Background Salt restriction may lower blood pressure variability (BPV), but previous studies have shown inconsistent results. Therefore, we investigated in an observational study and intervention trial whether urinary sodium excretion and salt intake are associated with 24-hour BPV. Methods and Results We used data from the cross-sectional population-based Maastricht Study (n=2652; 60±8 years; 52% men) and from a randomized crossover trial (n=40; 49±11 years; 33% men). In the observational study, we measured 24-hour urinary sodium excretion and 24-hour BPV and performed linear regression adjusted for age, sex, mean blood pressure, lifestyle, and cardiovascular risk factors. In the intervention study, participants adhered to a 7-day low- and high-salt diet (50 and 250 mmol NaCl/24 h) with a washout period of 14 days, 24-hour BPV was measured during each diet. We used linear mixed models adjusted for order of diet, mean blood pressure, and body mass index. In the observational study, 24-hour urinary sodium excretion was not associated with 24-hour systolic or diastolic BPV (β, per 1 g/24 h urinary sodium excretion: 0.05 mm Hg [95% CI, -0.02 to 0.11] and 0.04 mm Hg [95% CI, -0.01 to 0.09], respectively). In the intervention trial, mean difference in 24-hour systolic and diastolic BPV between the low- and high-salt diet was not statistically significantly different (0.62 mm Hg [95% CI, -0.10 to 1.35] and 0.04 mm Hg [95% CI, -0.54 to 0.63], respectively). Conclusions Urinary sodium excretion and salt intake are not independently associated with 24-hour BPV. These findings suggest that salt restriction is not an effective strategy to lower BPV in the White general population. Registration URL: https://clinicaltrials.gov/ct2/show/NCT02068781.

Comparative Pharmacokinetics/Pharmacodynamics of Fixed-Dose Combination of Esomeprazole and Calcium Carbonate (AD-206) to the Conventional Esomeprazole

Purpose

Proton pump inhibitors (PPIs) are used for the treatment of acid-related disorders. Demands for enhanced stability and faster onset led to the development of AD-206, a fixed-dose combination of a PPI (esomeprazole) with an antacid salt (calcium carbonate). This study compared the pharmacokinetics (PKs) and pharmacodynamics (PDs) of AD-206 (Addpharma) with conventional esomeprazole (Nexium^®, AstraZeneca).

Materials and Methods

A randomized, open-label, two-treatment, two-sequence crossover study was conducted with 2 different doses of esomeprazole at 20 and 40 mg with a fixed calcium carbonate dose of 600 mg in AD-206. Forty-four subjects were included in each dose group and randomly received either AD-206 or the conventional esomeprazole for 7 consecutive days in each period. After a single- and multiple-dose, blood samples for the PK analysis were analyzed, and 24-hour intragastric pH monitoring was conducted.

Results

The systemic exposure of esomeprazole after a multiple-dose of AD-206 was similar to that of the conventional esomeprazole in both doses, but the time to reach the peak concentration was faster in AD-206. The percentage decrease from baseline in the integrated gastric acidity for a 24-hour interval after the dose was not significantly different between the AD-206 and the conventional esomeprazole after a single- and multiple-dose for both doses, and the time to reach pH 4 was faster for AD-206.

Conclusion

AD-206 showed a similar systemic exposure and suppression of gastric acid secretion after a multiple-dose compared to the conventional esomeprazole.

Eating in the absence of hunger in children with mild sleep loss: a randomized crossover trial with learning effects

BACKGROUND

While insufficient sleep duration has emerged as a strong, independent risk factor for obesity, the mechanisms remain unclear. One possibility is greater "eating in the absence of hunger" (EAH) or energy intake beyond the point of satiety, when tired.

OBJECTIVE

The aim was to determine whether mild sleep loss increases EAH in children.

METHODS

A crossover study was undertaken in 105 healthy children (8-12 y) with normal sleep (∼8-11 h/night). After randomization, children went to bed 1 h earlier (sleep extension) or 1 h later (sleep restriction) than their usual bedtime, over 2 intervention weeks separated by a 1-wk washout. At the end of each intervention week, children underwent an EAH feeding experiment involving a preloading meal until satiation, followed by an ad libitum buffet (of highly palatable snacks) to measure EAH, with each food item weighed before and after consumption.

RESULTS

Ninety-three children completed the EAH experiment. There was no evidence of a difference in energy intake from EAH between sleep restriction and extension conditions when analyzed as a crossover design. However, a learning effect was found, with children eating significantly less (-239 kJ; 95% CI: -437, -41 kJ; P = 0.018) during the preload phase and significantly more (181 kJ; 95% CI: 38, 322 kJ; P = 0.013) in the ad libitum phase in the second week. No significant differences were seen using an underpowered parallel analysis for energy intake during the ad libitum phase when sleep deprived (106 kJ; 95% CI: -217, 431 kJ; P = 0.514).

CONCLUSIONS

Our findings suggest that measuring a difference in eating behavior in relation to sleep proved unsuitable using the EAH experiment in a crossover design in children, due to a learning effect. This trial was registered at the Australian New Zealand Clinical Trials Registry (http://www.anzctr.org.au/Trial/Registration/TrialReview.aspx?id=367587&isReview=true) as ACTRN12618001671257 .

Comparison between daily and on-demand PrEP (pre-exposure prophylaxis) regimen in covering condomless anal intercourse for men who have sex with men in Hong Kong: A randomized, controlled, open-label, crossover trial

Introduction

Both daily and on‐demand regimens have been proven effective for pre‐exposure prophylaxis (PrEP) against HIV in men who have sex with men (MSM). We aimed to compare the two regimens on their coverage of condomless anal intercourse (CLAI) in MSM.

Methods

A randomized, controlled, open‐label, crossover trial was conducted in a teaching hospital in Hong Kong. Participants were sexually active HIV‐negative MSM aged 18 years or above with normal renal function and without chronic hepatitis B infection. Oral tenofovir disoproxil fumarate 300 mg/emtricitabine 200 mg (TDF/FTC) tablets were prescribed for PrEP. After a 2‐week lead‐in with daily TDF/FTC for treatment‐naïve MSM for tolerance assessment, participants were randomly assigned in a 1:1 ratio with a block size of four to either daily‐first or on‐demand‐first arm based on the IPERGAY study, for receiving PrEP for 16 weeks, then crossed‐over to the alternative regimen for another 16 weeks. The primary outcome was the proportion of days with PrEP‐covered CLAI by intention‐to‐treat analysis. The trial is registered with the CCRB Clinical Trials Registry, CUHK, CUHK_CCRB00606, and is closed to accrual.

Results

Between 25 August 2018 and 23 March 2019, 119 eligible participants were assigned to daily‐first arm (n = 59) and on‐demand‐first arm (n = 60) with an 87% overall completion rate (n = 103). With 96% and 54% of days on PrEP during daily and on‐demand periods, respectively, the proportion of days with PrEP‐covered CLAI between two arms were not statistically different (92% vs. 92%, p = 0.93). About half (47%) were diagnosed with at least one episode of incident sexually transmitted infection. Mild and time‐limited adverse events, including diarrhoea, headache, nausea and dizziness, were reported in 37 (31%) and 10 (8%) during the daily and on‐demand periods, respectively. At the end of the study, a similar proportion favoured daily or on‐demand regimen.

Conclusions

High prevention‐effective adherence, as reflected from the coverage of CLAI, was achievable by either daily or on‐demand PrEP among MSM, albeit a higher number of tablets taken for daily PrEP. As both regimens were well accepted, a flexible approach adopting either or both regimens with possible switching is warranted in order to suit individual health needs.

Using Flow Disruptions to Examine System Safety in Robotic-Assisted Surgery: Protocol for a Stepped Wedge Crossover Design

BACKGROUND

The integration of high technology into health care systems is intended to provide new treatment options and improve the quality, safety, and efficiency of care. Robotic-assisted surgery is an example of high technology integration in health care, which has become ubiquitous in many surgical disciplines.

OBJECTIVE

This study aims to understand and measure current robotic-assisted surgery processes in a systematic, quantitative, and replicable manner to identify latent systemic threats and opportunities for improvement based on our observations and to implement and evaluate interventions. This 5-year study will follow a human factors engineering approach to improve the safety and efficiency of robotic-assisted surgery across 4 US hospitals.

METHODS

The study uses a stepped wedge crossover design with 3 interventions, introduced in different sequences at each of the hospitals over four 8-month phases. Robotic-assisted surgery procedures will be observed in the following specialties: urogynecology, gynecology, urology, bariatrics, general, and colorectal. We will use the data collected from observations, surveys, and interviews to inform interventions focused on teamwork, task design, and workplace design. We intend to evaluate attitudes toward each intervention, safety culture, subjective workload for each case, effectiveness of each intervention (including through direct observation of a sample of surgeries in each observational phase), operating room duration, length of stay, and patient safety incident reports. Analytic methods will include statistical data analysis, point process analysis, and thematic content analysis.

RESULTS

The study was funded in September 2018 and approved by the institutional review board of each institution in May and June of 2019 (CSMC and MDRH: Pro00056245; VCMC: STUDY 270; MUSC: Pro00088741). After refining the 3 interventions in phase 1, data collection for phase 2 (baseline data) began in November 2019 and was scheduled to continue through June 2020. However, data collection was suspended in March 2020 due to the COVID-19 pandemic. We collected a total of 65 observations across the 4 sites before the pandemic. Data collection for phase 2 was resumed in October 2020 at 2 of the 4 sites.

CONCLUSIONS

This will be the largest direct observational study of surgery ever conducted with data collected on 680 robotic surgery procedures at 4 different institutions. The proposed interventions will be evaluated using individual-level (workload and attitude), process-level (perioperative duration and flow disruption), and organizational-level (safety culture and complications) measures. An implementation science framework is also used to investigate the causes of success or failure of each intervention at each site and understand the potential spread of the interventions.

INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID)

DERR1-10.2196/25284.

A randomized phase 1b cross-over study of the safety of low-dose pioglitazone for treatment of autosomal dominant polycystic kidney disease

Background

Autosomal dominant polycystic kidney disease (ADPKD) is one of the most common monogenetic disorders in humans and is characterized by numerous fluid-filled cysts that grow slowly, resulting in end-stage renal disease in the majority of patients. Preclinical studies have indicated that treatment with low-dose thiazolidinediones, such as pioglitazone, decrease cyst growth in rodent models of PKD.

Methods

This Phase 1b cross-over study compared the safety of treatment with a low dose (15 mg) of the peroxisome proliferator-activated receptor-γ (PPAR-γ) agonist pioglitazone or placebo in PKD patients, with each treatment given for 1 year. The study monitored known side effects of PPAR-γ agonist treatment, including fluid retention and edema. Liver enzymes and risk of hypoglycemia were assessed throughout the study. As a secondary objective, the efficacy of low-dose pioglitazone was followed using a primary assessment of total kidney volume (TKV), blood pressure (BP) and kidney function.

Results

Eighteen patients were randomized and 15 completed both arms. Compared with placebo, allocation to pioglitazone resulted in a significant decrease in total body water as assessed by bioimpedance analysis {mean difference 0.16 Ω [95% confidence interval (CI) 0.24–2.96], P = 0.024} and no differences in episodes of heart failure, clinical edema or change in echocardiography. Allocation to pioglitazone led to no difference in the percent change in TKV of −3.5% (95% CI −8.4–1.4, P = 0.14), diastolic BP and microalbumin:creatinine ratio.

Conclusions

In this small pilot trial in people with ADPKD but without diabetes, pioglitazone 15 mg was found to be as safe as placebo. Larger and longer-term randomized trials powered to assess effects on TKV are needed.

Estimating individualized treatment regimes from crossover designs

The field of precision medicine aims to tailor treatment based on patient-specific factors in a reproducible way. To this end, estimating an optimal individualized treatment regime (ITR) that recommends treatment decisions based on patient characteristics to maximize the mean of a prespecified outcome is of particular interest. Several methods have been proposed for estimating an optimal ITR from clinical trial data in the parallel group setting where each subject is randomized to a single intervention. However, little work has been done in the area of estimating the optimal ITR from crossover study designs. Such designs naturally lend themselves to precision medicine since they allow for observing the response to multiple treatments for each patient. In this paper, we introduce a method for estimating the optimal ITR using data from a 2 × 2 crossover study with or without carryover effects. The proposed method is similar to policy search methods such as outcome weighted learning; however, we take advantage of the crossover design by using the difference in responses under each treatment as the observed reward. We establish Fisher and global consistency, present numerical experiments, and analyze data from a feeding trial to demonstrate the improved performance of the proposed method compared to standard methods for a parallel study design.

Lessons learned from conducting a pragmatic, randomized, crossover trial on robot-assisted gait training in children with cerebral palsy (PeLoGAIT)

PURPOSE

To investigate the effectiveness of outpatient robot-assisted gait training (RAGT) in ambulatory children with spastic cerebral palsy.

METHODS

Children were randomized to two different intervention sequences within a pragmatic crossover design. They performed five weeks of RAGT (3 sessions per week) and five weeks of usual care (UC). Dimension E of the Gross Motor Function Measure-88 (GMFM E) as the primary outcome as well as Dimension D (GMFM D), and timed walking tests were assessed before and after each treatment sequence and after a 5-week follow-up.

RESULTS

The trial was stopped early because of recruitment problems. We included 16 children with a mean age of 11.3 years (6.0-15.3 years). GMFM E median (IQR) change scores were -0.7 (-2.8 to 3.5) after RAGT and 0 (-2.4 to 2.4) after UC. Neither GMFM E nor any secondary outcome measure changed significantly after RAGT or UC, nor were any period, follow-up, or carry-over effects observable.

CONCLUSIONS

RAGT as a single intervention was not effective in improving walking abilities in the included children. It should be embedded in a holistic treatment approach, as it cannot cover all aspects relevant to gait. Furthermore, children's personalized rehabilitation goals should be carefully monitored with individualized measurement instruments.

Improving Oral Health in Older Adults and People With Disabilities: Protocol for a Community-Based Clinical Trial (Good Oral Health)

Background

Low-income older adults experience disparities in oral health problems, including caries and periodontal disease, that can exacerbate already high levels of chronic and acute health problems. Behavioral interventions have been shown to improve oral health status but are typically administered in institutional rather than community settings. Furthermore, multiple simultaneous interventions at different levels in the locations where people live and work are likely to have more impact and sustainability than single interventions in clinical settings.

Objective

This paper outlines a protocol for conducting a bilingual 5-year community-based trial of a bilevel intervention that addresses community norms, beliefs, intentions, and practices to improve oral health hygiene of vulnerable older adults living in publicly subsidized housing. The intervention utilizes (1) a face-to-face counseling approach (adapted motivational interviewing [AMI]) and (2) resident-run oral health campaigns in study buildings.

Methods

The study’s modified fractional factorial crossover design randomizes 6 matched buildings into 2 conditions: AMI followed by campaign (AB) and campaign followed by AMI (BA). The total intervention cycle is approximately 18 months in duration. The design compares the 2 interventions alone (T0-T1), and in different sequences (T1-T2), using a self-reported survey and clinical assessment to measure Plaque Score (PS) and Gingival Index (GI) as outcomes. A final timepoint (T3), 6 months post T2, assesses sustainability of each sequence. The intervention is based on the Fishbein integrated model that includes both individual and contextual modifiers, norms and social influence, beliefs, attitudes, efficacy, and intention as predictors of improvements in PS, GI, and oral health quality of life. The cognitive and behavioral domains in the intervention constitute the mechanisms through which the intervention should have a positive effect. They are tailored through the AMI and targeted to building populations through the peer-facilitated oral health campaigns. The sample size is 360, 180 in each condition, with an attrition rate of 25%. The study is funded by National Institute of Dental and Craniofacial Research (NIDCR) and has been reviewed by University of Connecticut and NIDCR institutional review boards and NIDCR’s clinical trials review procedures.

Results

When compared against each other, the face-to-face intervention is expected to have greater positive effects on clinical outcomes and oral health quality of life through the mediators. When sequences are compared, the results may be similar but affected by different mediators. The arm consisting of the BA is expected to have better sustainability. The protocol’s unique features include the comparative effectiveness crossover design; the introduction of new emotion-based mediators; the balancing of fidelity, tailoring, and targeting; and resident engagement in the intervention.

Conclusions

If successful, the evaluated interventions can be scaled up for implementation in other low-income congregate living and recreational settings with older adult collectives.

Trial Registration

ClinicalTrials.gov NCT02419144; https://clinicaltrials.gov/ct2/show/NCT02419144

International Registered Report Identifier (IRRID)

DERR1-10.2196/14555

Testing treatment-by-period interaction in four-period crossover trials

Statistical analyses of crossover clinical trials have mainly focused on assessing the treatment effect, carryover effect, and period effect. When a treatment-by-period interaction is plausible, it is important to test such interaction first before making inferences on differences among individual treatments. Considerably less attention has been paid to the treatment-by-period interaction, which has historically been aliased with the carryover effect in two-period or three-period designs. In this article, from the data of a newly developed four-period crossover design, we propose a statistical method to compare the effects of two active drugs with respect to two response variables. We study estimation and hypothesis testing considering the treatment-by-period interaction. Constrained least squares is used to estimate the treatment effect, period effect, and treatment-by-period interaction. For hypothesis testing, we extend a general multivariate method for analyzing the crossover design with multiple responses. Results from simulation studies have shown that this method performs very well. We also illustrate how to apply our method to the real data problem.

Moderate Postmeal Walking Has No Beneficial Effects Over Resting on Postprandial Lipemia, Glycemia, Insulinemia, and Selected Oxidative and Inflammatory Parameters in Older Adults with a Cardiovascular Disease Risk Phenotype: A Randomized Crossover Trial

BACKGROUND

Research suggests that postprandial events, as risk factors for cardiovascular diseases (CVDs), are influenced by meal composition and exercise.

OBJECTIVES

We investigated the effect of walking versus rest on postprandial metabolic, inflammatory, and oxidative events following the consumption of test meals reflecting 2 different dietary patterns in older adults with an increased CVD risk.

METHODS

A randomized crossover trial was conducted in 26 men and women (aged 70 ± 5 y; BMI 30.3 ± 2.3 kg/m2). Each adult participated in 4 treatments combining 1 of 2 iso-energetic (4300 kJ) meals [Western diet high-fat meal (WD): total fat, 59.4 g; saturated fatty acids, 32.0 g, dietary fiber, 4.2 g; or Mediterranean-type diet meal (MD): total fat, 40.1 g; saturated fatty acids, 5.1 g; dietary fiber, 14.5 g] with 30 min walking (4.6 ± 0.1 km/h) or rest. Primary (serum triglycerides) and secondary [serum nonesterified fatty acids (NEFAs); parameters of glucose metabolism, inflammation, endothelial activation, oxidation; blood pressure/heart rate] outcomes were measured at fasting and 1.5, 3.0, and 4.5 h postprandially. Data were analyzed by linear mixed models.

RESULTS

Triglycerides were higher after the WD than after the MD [AUC in mmol/L × min: Western diet high-fat meal plus postprandial walking (WD-W), 218 ± 15.2; Western diet high-fat meal plus postprandial resting (WD-R), 207 ± 12.6; Mediterranean-type diet meal plus postprandial walking (MD-W), 139 ± 9.83; Mediterranean-type diet meal plus postprandial resting (MD-R), 149 ± 8.15; P  < 0.001]. No meal or activity effect was observed for NEFAs based on AUC data (WD-W, -43.5 ± 7.08; WD-R, -49.2 ± 6.94; MD-W, -48.0 ± 11.6; MD-R, -67.6 ± 7.58). Plasma glucose was higher after the MD than after the WD (WD-W, 222 ± 34.9; WD-R, 177 ± 32.8; MD-W, 314 ± 44.4; MD-R, 275 ± 57.8; P  < 0.001), as was serum insulin (AUC in nmol/L × min: WD-W, 82.0 ± 10.3; WD-R, 88.6 ± 12.8; MD-W, 129 ± 14.7; MD-R, 138 ± 20.5; P < 0.001). Plasma IL-6 was higher after walking than after resting (AUC in pg/mL × min: WD-W, 72.0 ± 34.0; WD-R, 14.3 ± 38.8; MD-W, 70.8 ± 39.4; MD-R, 5.60 ± 26.0; P < 0.05). Plasma vitamin C was higher after the MD than after the WD (P < 0.001) and after walking than after resting (P < 0.05; AUC in mg/L × min: WD-W, -305 ± 59.6; WD-R, -396 ± 84.0; MD-W, 113 ± 56.4; MD-R, -44.5 ± 48.1). We observed no meal or activity effects on parameters of oxidation and endothelial adhesion molecules. Our data revealed no significant meal × activity effects on all outcomes.

CONCLUSIONS

In older adults with an increased CVD risk, the MD was associated with superior effects on several postprandial parameters (e.g., triglycerides), in comparison to the WD. Data revealed no relevant differences regarding the effects of postmeal walking and resting. None of the 4 treatments can be rated as superior regarding their acute effects on the shown postprandial metabolic, oxidative, and inflammatory parameters. The trial was registered at German Clinical Trials Register (DRKS; http://www.germanctr.de and http://www.drks.de) under identifier DRKS00012409.

Accounting for a decaying correlation structure in cluster randomized trials with continuous recruitment

A requirement for calculating sample sizes for cluster randomized trials (CRTs) conducted over multiple periods of time is the specification of a form for the correlation between outcomes of subjects within the same cluster, encoded via the within-cluster correlation structure. Previously proposed within-cluster correlation structures have made strong assumptions; for example, the usual assumption is that correlations between the outcomes of all pairs of subjects are identical ("uniform correlation"). More recently, structures that allow for a decay in correlation between pairs of outcomes measured in different periods have been suggested. However, these structures are overly simple in settings with continuous recruitment and measurement. We propose a more realistic "continuous-time correlation decay" structure whereby correlations between subjects' outcomes decay as the time between these subjects' measurement times increases. We investigate the use of this structure on trial planning in the context of a primary care diabetes trial, where there is evidence of decaying correlation between pairs of patients' outcomes over time. In particular, for a range of different trial designs, we derive the variance of the treatment effect estimator under continuous-time correlation decay and compare this to the variance obtained under uniform correlation. For stepped wedge and cluster randomized crossover designs, incorrectly assuming uniform correlation will underestimate the required sample size under most trial configurations likely to occur in practice. Planning of CRTs requires consideration of the most appropriate within-cluster correlation structure to obtain a suitable sample size.

Effect of Crossover in Oncology Clinical Trials on Evidence Levels in Early Benefit Assessment in Germany

BACKGROUND

In oncology clinical trials, crossover is used frequently but may lead to uncertainties regarding treatment effects.

OBJECTIVE

To investigate the handling of evidence from crossover trials by the European Medicines Agency (EMA) and the German Federal Joint Committee (G-BA).

METHODS

For oncology medicines with early benefit assessments before January 2015, presence of crossover, clinical data, EMA requests for additional data, and G-BA benefit ratings/evidence levels were analyzed from manufacturers' dossiers, G-BA appraisals, European Public Assessment Reports, and original publications.

RESULTS

Eleven of 21 benefit assessments included crossover trials. Significant intergroup differences (P < 0.05) in overall survival (OS) were noted in 7 of 11 trials with and 7 of 10 without crossover. For 6 of 11 medicines with crossover, these were demonstrated before crossover. Treatment effects generally worsened with increasing proportions of crossover. The EMA requested additional data more frequently if crossover was performed, particularly if no OS data were available before crossover. The G-BA granted a considerable benefit to 73% of medicines with crossover and 40% of those without. Evidence levels were intermediate for 50% and 75%, respectively. None of the medicines received the highest evidence level.

CONCLUSIONS

In G-BA appraisals, oncology medicines with crossover received better additional benefit ratings, but were assigned lower evidence levels, than those without. The five medicines with crossover after progression were assigned lower evidence levels than the six medicines with crossover after demonstration of superior OS, indicating that the way in which crossover is implemented may be one factor influencing the assignment of evidence levels by the G-BA.

Investigating the Impact of Hearing Aid Use and Auditory Training on Cognition, Depressive Symptoms, and Social Interaction in Adults With Hearing Loss: Protocol for a Crossover Trial

Background

Sensorineural hearing loss is the most common sensory deficit among older adults. Some of the psychosocial consequences of this condition include difficulty in understanding speech, depression, and social isolation. Studies have shown that older adults with hearing loss show some age-related cognitive decline. Hearing aids have been proven as successful interventions to alleviate sensorineural hearing loss. In addition to hearing aid use, the positive effects of auditory training—formal listening activities designed to optimize speech perception—are now being documented among adults with hearing loss who use hearing aids, especially new hearing aid users. Auditory training has also been shown to produce prolonged cognitive performance improvements. However, there is still little evidence to support the benefits of simultaneous hearing aid use and individualized face-to-face auditory training on cognitive performance in adults with hearing loss.

Objective

This study will investigate whether using hearing aids for the first time will improve the impact of individualized face-to-face auditory training on cognition, depression, and social interaction for adults with sensorineural hearing loss. The rationale for this study is based on the hypothesis that, in adults with sensorineural hearing loss, using hearing aids for the first time in combination with individualized face-to-face auditory training will be more effective for improving cognition, depressive symptoms, and social interaction rather than auditory training on its own.

Methods

This is a crossover trial targeting 40 men and women between 50 and 90 years of age with either mild or moderate symmetric sensorineural hearing loss. Consented, willing participants will be recruited from either an independent living accommodation or via a community database to undergo a 6-month intensive face-to-face auditory training program (active control). Participants will be assigned in random order to receive hearing aid (intervention) for either the first 3 or last 3 months of the 6-month auditory training program. Each participant will be tested at baseline, 3, and 6 months using a neuropsychological battery of computer-based cognitive assessments, together with a depression symptom instrument and a social interaction measure. The primary outcome will be cognitive performance with regard to spatial working memory. Secondary outcome measures include other cognition performance measures, depressive symptoms, social interaction, and hearing satisfaction.

Results

Data analysis is currently under way and the first results are expected to be submitted for publication in June 2018.

Conclusions

Results from the study will inform strategies for aural rehabilitation, hearing aid delivery, and future hearing loss intervention trials.

Trial Registration

ClinicalTrials.gov NCT03112850; https://clinicaltrials.gov/ct2/show/NCT03112850 (Archived by WebCite at http://www.webcitation.org/6xz12fD0B).

A Randomized, Double Blind, Placebo Controlled, Crossover Study to Assess the Safety and Beneficial Effects of Cassia Tora Supplementation in Healthy Adults

OBJECTIVE

The current clinical trial was aimed at evaluating the safety and beneficial effect of Cassia tora (C. tora) supplementation in healthy adults.

DESIGN

A randomized, double blind, placebo controlled study with a crossover design was done on 60 healthy normal weight adults (age range: 20-55 yrs). The study consisted of 2 treatment phases of 24 weeks each with a washout period of 4 weeks between the phases. 30 subjects randomly allocated to the 'Placebo first' group and 30 to 'C. tora first' group and assigned to receive a dose of C. tora (330 mg) or matched placebo three times a day. Safety markers were measured at base line and at the end of both the treatment phases. Body mass index, blood pressure, fasting blood sugar, glycated hemoglobin, lipid profile and antioxidants were measured at baseline and at every three months interval. Repeated measures analysis was applied to assess the period and carryover effects of the drug over placebo on biochemistries.

RESULTS

C. tora supplementation was well tolerated and no apparent changes were observed in safety markers. The net effect of C. tora in natural units over placebo was 0.83 [0.57, 1.09]- high density lipoprotein cholesterol; 27.63 [24.39, 30.88]- superoxide dismutase; 0.32 [0.28, 0.36]- catalase; 0.68 [0.56, 0.80]- glutathione peroxidase; 0.25 [0.22, 0.29]- glutathione s-transferase; 0.32 [0.29, 0.36]- glutathione and -1.08 [-1.63, -0.54]- low density lipoprotein cholesterol.

CONCLUSION

The findings advocate that C. tora supplementation is safe and beneficial in elevating high density lipoprotein cholesterol and antioxidants and hence advised for consumption.

Testing for bioequivalence of highly variable drugs from TR-RT crossover designs with heterogeneous residual variances

Traditional bioavailability studies assess average bioequivalence (ABE) between the test (T) and reference (R) products under the crossover design with TR and RT sequences. With highly variable (HV) drugs whose intrasubject coefficient of variation in pharmacokinetic measures is 30% or greater, assertion of ABE becomes difficult due to the large sample sizes needed to achieve adequate power. In 2011, the FDA adopted a more relaxed, yet complex, ABE criterion and supplied a procedure to assess this criterion exclusively under TRR-RTR-RRT and TRTR-RTRT designs. However, designs with more than 2 periods are not always feasible. This present work investigates how to evaluate HV drugs under TR-RT designs. A mixed model with heterogeneous residual variances is used to fit data from TR-RT designs. Under the assumption of zero subject-by-formulation interaction, this basic model is comparable to the FDA-recommended model for TRR-RTR-RRT and TRTR-RTRT designs, suggesting the conceptual plausibility of our approach. To overcome the distributional dependency among summary statistics of model parameters, we develop statistical tests via the generalized pivotal quantity (GPQ). A real-world data example is given to illustrate the utility of the resulting procedures. Our simulation study identifies a GPQ-based testing procedure that evaluates HV drugs under practical TR-RT designs with desirable type I error rate and reasonable power. In comparison to the FDA's approach, this GPQ-based procedure gives similar performance when the product's intersubject standard deviation is low (≤0.4) and is most useful when practical considerations restrict the crossover design to 2 periods.

Persistent threats to validity in single-group interrupted time series analysis with a cross over design

RATIONALE, AIMS AND OBJECTIVES

The basic single-group interrupted time series analysis (ITSA) design has been shown to be susceptible to the most common threat to validity-history-the possibility that some other event caused the observed effect in the time series. A single-group ITSA with a crossover design (in which the intervention is introduced and withdrawn 1 or more times) should be more robust. In this paper, we describe and empirically assess the susceptibility of this design to bias from history.

METHOD

Time series data from 2 natural experiments (the effect of multiple repeals and reinstatements of Louisiana's motorcycle helmet law on motorcycle fatalities and the association between the implementation and withdrawal of Gorbachev's antialcohol campaign with Russia's mortality crisis) are used to illustrate that history remains a threat to ITSA validity, even in a crossover design.

RESULTS

Both empirical examples reveal that the single-group ITSA with a crossover design may be biased because of history. In the case of motorcycle fatalities, helmet laws appeared effective in reducing mortality (while repealing the law increased mortality), but when a control group was added, it was shown that this trend was similar in both groups. In the case of Gorbachev's antialcohol campaign, only when contrasting the results against those of a control group was the withdrawal of the campaign found to be the more likely culprit in explaining the Russian mortality crisis than the collapse of the Soviet Union.

CONCLUSIONS

Even with a robust crossover design, single-group ITSA models remain susceptible to bias from history. Therefore, a comparable control group design should be included, whenever possible.

A Randomized Crossover Trial of Dietary Sodium Restriction in Stage 3-4 CKD

BACKGROUND AND OBJECTIVES

Patients with chronic kidney disease (CKD) are often volume expanded and hypertensive. Few controlled studies have assessed the effects of a sodium-restricted diet (SRD) in CKD.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

We conducted a randomized crossover trial to evaluate the effect of SRD (target <2 g sodium per day) versus usual diet on hydration status (by bioelectrical impedance spectroscopy) and blood pressure (BP) between May of 2009 and May of 2013. A total of 58 adults with stage 3-4 CKD were enrolled from two academic sites: University of Michigan (n=37) and University of North Carolina at Chapel Hill (n=21); 60% were men, 43% were diabetic, 93% were hypertensive, and mean age was 61 years. Participants followed SRD or usual diet for 4 weeks, followed by a 2-week washout period and a 4-week crossover phase. During the SRD, dieticians provided counseling every 2 weeks, using motivational interviewing techniques.

RESULTS

Whole-body extracellular volume and calf intracellular volume decreased by 1.02 L (95% confidence interval [95% CI], -1.48 to -0.56; P<0.001) and -0.06 L (95% CI, -0.12 to -0.01; P=0.02), respectively, implying decreased fluid content on the SRD compared with usual diet. Significant reductions in urinary sodium (-57.3 mEq/24 h; 95% CI, -81.8 to -32.9), weight (-2.3 kg; 95% CI, -3.2 to -1.5), and 24-hour systolic BP (-10.8 mmHg; 95% CI, -17.0 to -4.6) were also observed (all P<0.01). Albumin-to-creatinine ratio did not change significantly and mean serum creatinine increased slightly (0.1 mg/dl; 95% CI, -0.01 to 0.2; P=0.06). No period or carryover effects were observed. Results were similar when analyzed from phase 1 only before crossover, although P values were modestly larger because of the loss of power.

CONCLUSIONS

In this randomized crossover trial, implementation of SRD in patients with CKD stage 3-4 resulted in clinically and statistically significant improvement in BP and hydration status. This simple dietary intervention merits a larger trial in CKD to evaluate effects on major clinical outcomes.

BDNF Responses in Healthy Older Persons to 35 Minutes of Physical Exercise, Cognitive Training, and Mindfulness: Associations with Working Memory Function

Brain-derived neurotrophic factor (BDNF) has a central role in brain plasticity by mediating changes in cortical thickness and synaptic density in response to physical activity and environmental enrichment. Previous studies suggest that physical exercise can augment BDNF levels, both in serum and the brain, but no other study has examined how different types of activities compare with physical exercise in their ability to affect BDNF levels. By using a balanced cross over experimental design, we exposed nineteen healthy older adults to 35-minute sessions of physical exercise, cognitive training, and mindfulness practice, and compared the resulting changes in mature BDNF levels between the three activities. We show that a single bout of physical exercise has significantly larger impact on serum BDNF levels than either cognitive training or mindfulness practice in the same persons. This is the first study on immediate BDNF effects of physical activity in older healthy humans and also the first study to demonstrate an association between serum BDNF responsivity to acute physical exercise and working memory function. We conclude that the BDNF increase we found after physical exercise more probably has a peripheral than a central origin, but that the association between post-intervention BDNF levels and cognitive function could have implications for BDNF responsivity in serum as a potential marker of cognitive health.

An objective Bayesian analysis of a crossover design via model selection and model averaging

Inference about the treatment effect in a crossover design has received much attention over time owing to the uncertainty in the existence of the carryover effect and its impact on the estimation of the treatment effect. Adding to this uncertainty is that the existence of the carryover effect and its size may depend on the presence of the treatment effect and its size. We consider estimation and testing hypothesis about the treatment effect in a two-period crossover design, assuming normally distributed response variable, and use an objective Bayesian approach to test the hypothesis about the treatment effect and to estimate its size when it exists while accounting for the uncertainty about the presence of the carryover effect as well as the treatment and period effects. We evaluate and compare the performance of the proposed approach with a standard frequentist approach using simulated data, and real data. Copyright © 2016 John Wiley & Sons, Ltd.

Crossover design and its application in late-phase diabetes studies

Crossover design has been widely used in late-phase clinical studies, as well as in pharmacokinetic and pharmacodynamic, bioequivalence, and medical device studies; however, its interpretability and applicability continue to be debated. Herein we provide discussions around a crossover design's scientific benefit, applicability, and how it can be implemented in late-phase diabetes studies by properly handling key issues: carryover effect, washout period, and baseline selection. Specifically, detailed considerations are provided about the validity and situations of having appropriate length of study duration to deal with carryover effects so that a washout period may not be needed. A simulation study and data mining results on 12 crossover late-phase insulin clinical trials are presented to examine the discussion points and proposals.

Comparison of Effect of Two-Hour Exposure to Forest and Urban Environments on Cytokine, Anti-Oxidant, and Stress Levels in Young Adults

The purpose of this study was to investigate the effect of two-hour exposure to a forest environment on cytokine, anti-oxidant and stress levels among university students and to compare the results to those measured in urban environments. Forty-one subjects were recruited. For our crossover design, subjects were divided into two groups based on similar demographic characteristics. Group A remained in the urban environment and was asked to perform regular breathing for 2 h. Blood samples were collected and the serum levels of cytokines including interleukin-6 (IL-6), IL-8, tumor necrosis factor-α (TNF-α), and glutathione peroxidase (GPx) were examined. Subjects were moved to a small town in a rural area for an equal amount of time to exclude carryover effects, and then remained for another 2 h in a forest environment. The second set of blood samples was collected to assess the effect of exposure to the forest environment. Using the same method, Group B was first exposed to the forest environment, followed by exposure to the urban environment. Blood samples collected after the subjects were exposed to the forest environment showed significantly lower levels of IL-8 and TNF-α compared to those in samples collected after urban environment exposure (10.76 vs. 9.21, t = 4.559, p < 0.001, and 0.97 vs. 0.87, t = 4.130, p < 0.001). The GPx concentration increased significantly after exposure to the forest environment (LnGPx = 5.09 vs. LnGPx = 5.21, t = −2.039, p < 0.05).

Test-retest reliability and effects of repeated testing and satiety on performance of an Emotional Test Battery

The P1vital® Oxford Emotional Test Battery (ETB) comprises five computerized tasks designed to assess cognition and emotional processing in human participants. It has been used in between-subjects experimental designs; however, it is unclear whether the battery can be used in crossover designs. This is of particular importance given the increasing use of ETB tasks for repeated assessment of depressed patients in clinical trials and clinical practice. In addition, although satiety state has been reported to affect performance on some cognitive and emotional tasks, it is not known whether it can influence performance on the ETB. Two studies explored these issues. In Experiment 1, 30 healthy women were tested on the ETB on 4 separate occasions (each a week apart) in a within-subjects design. In Experiment 2, another 30 healthy women were randomized to either a satiated or a hungry condition, where they were given an ad libitum lunch of cheese sandwiches, before (satiated) or after (hungry) they were asked to complete the ETB. Experiment 1 demonstrated good test–retest reliability for the ETB. One of the tasks was free from practice effects, whilst performance on the other four tasks stabilized after the first two sessions. In Experiment 2, eating to satiety only affected performance on a single ETB task. These results suggest that the ETB can be used in crossover designs after two initial training sessions. Further, as a robust satiety manipulation had only a limited effect on a single ETB task, it is unlikely that appetitive state will confound ETB performance.

Carryover negligibility and relevance in bioequivalence studies

The carryover effect is a recurring issue in the pharmaceutical field. It may strongly influence the final outcome of an average bioequivalence study. Testing a null hypothesis of zero carryover is useless: not rejecting it does not guarantee the non-existence of carryover, and rejecting it is not informative of the true degree of carryover and its influence on the validity of the final outcome of the bioequivalence study. We propose a more consistent approach: even if some carryover is present, is it enough to seriously distort the study conclusions or is it negligible? This is the central aim of this paper, which focuses on average bioequivalence studies based on 2 × 2 crossover designs and on the main problem associated with carryover: type I error inflation. We propose an equivalence testing approach to these questions and suggest reasonable negligibility or relevance limits for carryover. Finally, we illustrate this approach on some real datasets.

"First-wave" bias when conducting active safety monitoring of newly marketed medications with outcome-indexed self-controlled designs

Large health care databases are used extensively for pharmacoepidemiologic studies. Unique methodological issues arise when applying self-controlled designs (i.e., using within-person comparisons) for active surveillance of newly marketed drugs. We use 3 examples to illustrate bias related to population-level exposure time trends when using outcome-indexed self-controlled (i.e., case-crossover) designs for active surveillance and evaluate the ability of the case-time-control design to adjust for bias from population-level exposure time trends. We mimicked active surveillance by conducting sequential analyses after market entry for 3 medications and outcomes (valdecoxib for myocardial infarction (MI), aripiprazole for MI, and telithromycin for acute liver failure) using Medicaid Analytic eXtracts (from all 50 US states, 2000-2006). The case-crossover exposure odds ratio (EOR) in the months immediately following valdecoxib market entry implausibly suggested a 12-fold higher risk of MI during exposed time relative to unexposed time; among age-, sex-, and time-matched controls, the corresponding EOR of 4.5 indicated strong population-level exposure time trends. Over subsequent monitoring periods, case-crossover EORs rapidly dropped to 1.4. Adjustment for bias from population-level exposure time trends with the case-time-control analysis resulted in more consistent associations between valdecoxib and MI across sequential monitoring periods. Similar results were observed in each example. Strong population-level exposure time trends can bias case-crossover studies conducted among "first-wave" users of newly marketed medications. Suggested strategies can help assess and adjust for population-level exposure time trends.

New approach to assess bioequivalence parameters using generalized gamma mixed-effect model (model-based asymptotic bioequivalence test)

In the pharmacokinetic (PK) study under a 2x2 crossover design that involves both the test and reference drugs, we propose a mixed-effects model for the drug concentration-time profiles obtained from subjects who receive different drugs at different periods. In the proposed model, the drug concentrations repeatedly measured from the same subject at different time points are distributed according to a multivariate generalized gamma distribution, and the drug concentration-time profiles are described by a compartmental PK model with between-subject and within-subject variations. We then suggest a bioequivalence test based on the estimated bioavailability parameters in the proposed mixed-effects model. The results of a Monte Carlo study further show that the proposed model-based bioequivalence test is not only better on maintaining its level but also more powerful for detecting the bioequivalence of the two drugs than the conventional bioequivalence test based on a non-compartmental analysis or the one based on a mixed-effects model with a normal error variable. The application of the proposed model and test is finally illustrated by using data sets in two PK studies.

Notes on testing equality and interval estimation in Poisson frequency data under a three-treatment three-period crossover trial

When the frequency of event occurrences follows a Poisson distribution, we develop procedures for testing equality of treatments and interval estimators for the ratio of mean frequencies between treatments under a three-treatment three-period crossover design. Using Monte Carlo simulations, we evaluate the performance of these test procedures and interval estimators in various situations. We note that all test procedures developed here can perform well with respect to Type I error even when the number of patients per group is moderate. We further note that the two weighted-least-squares (WLS) test procedures derived here are generally preferable to the other two commonly used test procedures in the contingency table analysis. We also demonstrate that both interval estimators based on the WLS method and interval estimators based on Mantel-Haenszel (MH) approach can perform well, and are essentially of equal precision with respect to the average length. We use a double-blind randomized three-treatment three-period crossover trial comparing salbutamol and salmeterol with a placebo with respect to the number of exacerbations of asthma to illustrate the use of these test procedures and estimators.

Review of clinical trials for mitochondrial disorders: 1997-2012

Over the last 15 years, some 16 open and controlled clinical trials for potential treatments of mitochondrial diseases have been reported or are in progress, and are summarized and reviewed herein. These include trials of administering dichloroacetate (an activator of pyruvate dehydrogenase complex), arginine or citrulline (precursors of nitric oxide), coenzyme Q10 (CoQ10; part of the electron transport chain and an antioxidant), idebenone (a synthetic analogue of CoQ10), EPI-743 (a novel oral potent 2-electron redox cycling agent), creatine (a precursor of phosphocreatine), combined administration (of creatine, α-lipoate, and CoQ10), and exercise training (to increase muscle mitochondria). These trials have included patients with various mitochondrial disorders, a selected subcategory of mitochondrial disorders, or specific mitochondrial disorders (Leber hereditary optic neuropathy or mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes). The trial designs have varied from open-label/uncontrolled, open-label/controlled, or double-blind/placebo-controlled/crossover. Primary outcomes have ranged from single, clinically-relevant scores to multiple measures. Eight of these trials have been well-controlled, completed trials. Of these only 1 (treatment with creatine) showed a significant change in primary outcomes, but this was not reproduced in 2 subsequent trials with creatine with different patients. One trial (idebenone treatment of Leber hereditary optic neuropathy) did not show significant improvement in the primary outcome, but there was significant improvement in a subgroup of patients. Despite the paucity of benefits found so far, well-controlled clinical trials are essential building blocks in the continuing search for more effective treatment of mitochondrial disease, and current trials based on information gained from these prior experiences are in progress. Because of difficulties in recruiting sufficient mitochondrial disease patients and the relatively large expense of conducting such trials, advantageous strategies include crossover designs (where possible), multicenter collaboration, and the selection of very few, clinically relevant, primary outcomes.

Analysis of Poisson frequency data under a simple crossover trial

When the frequency of occurrence for an event of interest follows a Poisson distribution, we develop asymptotic and exact procedures for testing non-equality, non-inferiority and equivalence, as well as asymptotic and exact interval estimators for the ratio of mean frequencies between two treatments under a simple crossover design. Using Monte Carlo simulations, we evaluate the performance of these test procedures and interval estimators in a variety of situations. We note that all asymptotic test procedures developed here can generally perform well with respect to Type I error and can be preferable to the exact test procedure with respect to power if the number of patients per group is moderate or large. We further find that in these cases the asymptotic interval estimator with the logarithmic transformation can be more precise than the exact interval estimator without sacrificing the accuracy with respect to the coverage probability. However, the exact test procedure and exact interval estimator can be of use when the number of patients per group is small. We use a double-blind randomized crossover trial comparing salmeterol with a placebo in exacerbations of asthma to illustrate the practical use of these estimators.

Submitted for your consideration: potential advantages of a novel clinical trial design and initial patient reaction

In many circumstances, individuals do not respond identically to the same treatment. This phenomenon, which is called treatment response heterogeneity (TRH), appears to be present in treatments for many conditions, including obesity. Estimating the total amount of TRH, predicting an individual's response, and identifying the mediators of TRH are of interest to biomedical researchers. Clinical investigators and physicians commonly postulate that some of these mediators could be genetic. Current designs can estimate TRH as a function of specific, measurable observed factors; however, they cannot estimate the total amount of TRH, nor provide reliable estimates of individual persons' responses. We propose a new repeated randomizations design (RRD), which can be conceived as a generalization of the Balaam design, that would allow estimates of that variability and facilitate estimation of the total amount of TRH, prediction of an individual's response, and identification of the mediators of TRH. In a pilot study, we asked 118 subjects entering a weight loss trial for their opinion of the RRD, and they stated a preference for the RRD over the conventional two-arm parallel groups design. Research is needed as to how the RRD will work in practice and its relative statistical properties, and we invite dialog about it.

A diet based on multiple functional concepts improves cardiometabolic risk parameters in healthy subjects

BACKGROUND

Different foods can modulate cardiometabolic risk factors in persons already affected by metabolic alterations. The objective of this study was to assess, in healthy overweight individuals, the impact of a diet combining multiple functional concepts on risk markers associated with cardiometabolic diseases (CMD).

METHODS

Fourty-four healthy women and men (50-73 y.o, BMI 25-33, fasting glycemia ≤ 6.1 mmol/L) participated in a randomized crossover intervention comparing a multifunctional (active) diet (AD) with a control diet (CD) devoid of the "active" components. Each diet was consumed during 4 wk with a 4 wk washout period. AD included the following functional concepts: low glycemic impact meals, antioxidant-rich foods, oily fish as source of long-chain omega-3 fatty acids, viscous dietary fibers, soybean and whole barley kernel products, almonds, stanols and a probiotic strain (Lactobacillus plantarum Heal19/DSM15313).

RESULTS

Although the aim was to improve metabolic markers without promoting body weight loss, minor weight reductions were observed with both diets (0.9-1.8 ± 0.2%; P < 0.05). CD did not modify the metabolic variables measured. AD promoted significant changes in total serum cholesterol (-26 ± 1% vs baseline; P < 0.0001), LDL-cholesterol (-34 ± 1%; P < 0.0001), triglycerides (-19 ± 3%; P = 0.0056), LDL/HDL (-27 ± 2%; P < 0.0001), apoB/apoA1 (-10 ± 2%; P < 0.0001), HbA1c (-2 ± 0.4%; P = 0.0013), hs-CRP (-29 ± 9%; P = 0.0497) and systolic blood pressure (-8 ± 1%¸ P = 0.0123). The differences remained significant after adjustment for weight change. After AD, the Framingham cardiovascular risk estimate was 30 ± 4% (P < 0.0001) lower and the Reynolds cardiovascular risk score, which considers CRP values, decreased by 35 ± 3% (P < 0.0001).

CONCLUSION

The improved biomarker levels recorded in healthy individuals following the multifunctional regime suggest preventive potential of this dietary approach against CMD.

A semi-parametric approach to the frequency of occurrence under a simple crossover trial

To analyze the frequency of occurrence for an event of interest in a crossover design, we propose a semi-parametric approach. We develop two point estimators and four interval estimators in closed forms for the treatment effect under a random effects multiplicative risk model. Using Monte Carlo simulations, we evaluate these estimators and compare the four interval estimators with the classical interval estimator suggested elsewhere in a variety of situations. We note that the point estimator using the ratio of two arithmetic averages of mean frequencies under a multiplicative risk model can be comparable to the point estimator using the ratio of two geometric averages of mean frequencies. We note that as long as the number of patients per group is large, all the four interval estimators developed here can perform well. We also note that the classical interval estimator derived under the commonly assumed Poisson distribution for the frequency data can be conservative and lose precision if the Poisson distribution assumption is violated. We use a double-blind randomized crossover trial comparing salmeterol with a placebo in exacerbations of asthma to illustrate the practical use of these estimators.

Crossover studies with survival outcomes

Crossover designs are well known to have major advantages when comparing the effect of two treatments which do not interact. With a right-censored survival endpoint, however, this design is quickly abandoned in favour of the more costly parallel design. Motivated by human immunodeficiency virus (HIV) prevention studies which lacked power, we evaluate what may be gained in this setting and compare parallel with crossover designs. In a heterogeneous population, we find and explain a substantial increase in power for the crossover study using a non-parametric logrank test. With frailties in a proportional hazards model, crossover designs equally lead to substantially smaller variance for the subject-specific hazard ratio (HR), while the population-averaged HR sees negligible gain. Its efficiency benefit is recovered when the population-averaged HR is reconstructed from estimated subject-specific hazard rates. We derive the time point for treatment crossover that optimizes efficiency and end with the analysis of two recent HIV prevention trials. We find that a Cellulose sulphate trial could have hardly gained efficiency from a crossover design, while a Nonoxynol-9 trial stood to gain substantial power. We conclude that there is a role for effective crossover designs in important classes of survival problems.

To what extent do mass media health messages trigger patients' contacts with their GPs?

BACKGROUND

A recent Cochrane review concluded that mass media intervention may play an important role in influencing the use of health services, but little is known about the effects of unplanned untargeted information in the media.

AIM

To investigate the influence of messages in mass media about health issues on patients' contacts with their GPs.

DESIGN OF STUDY

A case crossover design study comparing the frequency of receiving mass media health messages in a period before contact with a GP versus the frequency in matching control time periods for the same individuals. The outcome measure was the odds of patients having received health messages in the period before they contacted their GP, compared to the odds in the control periods.

SETTING

The practices of 21 single-handed Danish GPs.

METHOD

Three hundred and twenty-two patients between 18 and 91 years of age were interviewed by telephone after an unscheduled contact with a GP, and 148 patients were interviewed again 3-6 months later. Health media messages were only recorded if patients could remember the topics.

RESULT

More than a third (35%) of the patients remembered receiving health media messages in the week before contact. No significant relationship (odds ratio = 1.2, 95% confidence interval = 0.5 to 2.6) between health messages and contact with GPs could be observed.

CONCLUSION

In the absence of health campaigns and drug advertisements, mass media health messages seldom directly trigger patients to consult their GPs.