Testing and estimation of purely nonparametric effects in repeated measures designs

A novel longitudinal rank-sum test for multiple primary endpoints in clinical trials: Applications to neurodegenerative disorders

Neurodegenerative disorders such as Alzheimer's disease (AD) present a significant global health challenge, characterized by cognitive decline, functional impairment, and other debilitating effects. Current AD clinical trials often assess multiple longitudinal primary endpoints to comprehensively evaluate treatment efficacy. Traditional methods, however, may fail to capture global treatment effects, require larger sample sizes due to multiplicity adjustments, and may not fully exploit multivariate longitudinal data. To address these limitations, we introduce the Longitudinal Rank Sum Test (LRST), a novel nonparametric rank-based omnibus test statistic. The LRST enables a comprehensive assessment of treatment efficacy across multiple endpoints and time points without multiplicity adjustments, effectively controlling Type I error while enhancing statistical power. It offers flexibility against various data distributions encountered in AD research and maximizes the utilization of longitudinal data. Extensive simulations and real-data applications demonstrate the LRST's performance, underscoring its potential as a valuable tool in AD clinical trials. Nonparametrics, Global test, rank-sum-type test, U-Statistics.

Estimation and Testing of Wilcoxon–Mann–Whitney Effects in Factorial Clustered Data Designs

Clustered data arise frequently in many practical applications whenever units are repeatedly observed under a certain condition. One typical example for clustered data are animal experiments, where several animals share the same cage and should not be assumed to be completely independent. Standard methods for the analysis of such data are Linear Mixed Models and Generalized Estimating Equations—however, checking their assumptions is not easy, especially in scenarios with small sample sizes, highly skewed, count, and ordinal or binary data. In such situations, Wilcoxon–Mann–Whitney type effects are suitable alternatives to mean-based or other distributional approaches. Hence, no specific data distribution, symmetric or asymmetric, is required. Within this work, we will present different estimation techniques of such effects in clustered factorial designs and discuss quadratic- and multiple contrast type-testing procedures for hypotheses formulated in terms of Wilcoxon–Mann–Whitney effects. Additionally, the framework allows for the occurrence of missing data: estimation and testing hypotheses are based on all-available data instead of complete-cases. An extensive simulation study investigates the precision of the estimators and the behavior of the test procedures in terms of their type-I error control. One real world dataset exemplifies the applicability of the newly proposed procedures.

Ranking procedures for repeated measures designs with missing data: Estimation, testing and asymptotic theory

We develop purely nonparametric methods for the analysis of repeated measures designs with missing values. Hypotheses are formulated in terms of purely nonparametric treatment effects. In particular, data can have different shapes even under the null hypothesis and therefore, a solution to the nonparametric Behrens-Fisher problem in repeated measures designs will be presented. Moreover, global testing and multiple contrast test procedures as well as simultaneous confidence intervals for the treatment effects of interest will be developed. All methods can be applied for the analysis of metric, discrete, ordinal, and even binary data in a unified way. Extensive simulation studies indicate a satisfactory control of the nominal type-I error rate, even for small sample sizes and a high amount of missing data (up to 30%). We apply the newly developed methodology to a real data set, demonstrating its application and interpretation.

The place of S-ketamine in fibromyalgia treatment (ESKEFIB): study protocol for a prospective, single-center, double-blind, randomized, parallel-group, dose-escalation controlled trial

Background

Fibromyalgia is a chronic multidimensional pain disease with no curative treatment currently available. Its management relies on a multimodal approach involving pharmacologic and non-pharmacologic elements. Because a suggested factor in its etiology is a central sensitization phenomenon involving the N-methyl-D-aspartate receptor (NMDAR), NMDAR antagonists have been proposed as a treatment target. Ketamine and its levogyre form, S-ketamine, have been used to treat chronic pain for many years without consensus about their therapeutic efficiency. We aim to assess the efficacy of S-ketamine as a co-treatment for fibromyalgia.

Methods

This prospective, randomized, single-center, double-blind, parallel-group, dose-escalation trial will compare a co-treatment with S-ketamine (intervention) to a control treatment without S-ketamine (control). It will consist of two successive cohorts with 2:1 randomization ratio (S-ketamine at two different doses: control) with 105 participants in each cohort. The protocol follow-up time will be 12 weeks, including 3 visits for the treatment (week 0, week 2, and week 4) and 3 visits for follow-up (week 6, week 9, and week 12). Our primary outcome, pain relief and/or better patient function, will be assessed with the Brief Pain Inventory questionnaire. The statistical analysis will be performed on an intention-to-treat basis. If the primary outcome is reached at the end of follow-up in the first cohort with low-dose S-ketamine (0.2 mg/kg), the trial will end. If not, the trial will continue with the second cohort and high-dose S-ketamine (0.4 mg/kg).

Discussion

The challenge of our trial is the inclusion of a large number of participants in comparison to other trials involving ketamine or S-ketamine infusions for chronic pain management. The originality of our protocol is to include functionality in addition to pain relief as a primary outcome because these two endpoints are not linked in a linear way. For some patients, functional status is more important than pain relief.

Trial registration

EudraCT reference: 2020-000473-25, ClinicalTrials.gov: NCT04436250, first posted June 18, 2020; last updated July 21, 2020. Protocol version 2.2 issued on September 30, 2020, after a revision by the ethics committee. https://clinicaltrials.gov/ct2/show/NCT04436250

Supplementary Information

The online version contains supplementary material available at 10.1186/s13063-021-05814-4.

Assessment of metacognition in aviation pilot students during simulated flight training of a demanding maneuver

This study adapted the Demand Resource Evaluation Scores (DRES) as a metacognitive indicator in assessing pilot students' perceptions during simulated training of a novel maneuver. Typically, positive DRES are associated with perceiving a demanding situation as a challenge and with improved performance, while negative DRES are linked to a perception of the situation as a threat, and to poorer performance. The novelty here was to assess DRES before and after the task and across three missions. Overall, students were found to change their perceptions from threat to challenge over time. Also, increased DRES were positively correlated with performance progressing from mission to mission, indicating that the students reflect on their performance as they advance in their training. These findings show that individual metacognitive evaluations of a stressful aviation maneuver might be important for the progress in performance. The results are discussed in terms of flight safety and pilot training.

Semi-automated kinetic perimetry: Comparison of the Octopus 900 and Humphrey visual field analyzer 3 versus Goldmann perimetry

PURPOSE

To evaluate the clinical usefulness and reproducibility of (semi-)automated kinetic perimetry of the Octopus 900 and Humphrey field analyzer 3 (HFA3) compared to Goldmann perimetry as reference technique.

METHODS

A prospective interventional study of two study groups, divided into three subgroups. The first study group consisted of 28 patients, performing one visual field examination on each of the three devices. A second group of 30 patients performed four examinations, one on Goldmann and three on Octopus 900 with the following testing strategies: (1) with reaction time (RT) vector, no headphone; (2) without RT vector, no headphone; and (3) without RT vector, with headphone. Comparisons for V4e and I4e stimuli were made of the mean isopter radius (MIR) and of the distances of the isopter to the central visual axis in four directions. Statistical analysis was made with the R software version 3.2.2.

RESULTS

For V4e stimuli, the mean isopter radius showed no statistic significant difference comparing Goldmann to HFA3 [p-value = 0.144; confidence interval (CI) -0.152 to 0.019] and comparing Goldmann to Octopus 900 without RT vector, either with (p-value = 0.347; CI -0.023 to 0.081) or without headphone (p-value = 0.130; CI -0.011 to 0.095). Octopus 900 with RT vector produced a significantly larger MIR for V4e stimuli in comparison to Goldmann (p-value < 0.001). I4e stimuli produced statistically significantly larger visual field areas when comparing HFA3 and Octopus 900 to Goldmann perimetry.

CONCLUSION

Humphrey field analyzer 3 and Octopus 900 without RT vector are promising successors of Goldmann perimetry.

Self-reported difficulty and preferences of wheeled mobility device users for simulated low-floor bus boarding, interior circulation and disembarking

BACKGROUND

Low ridership of public transit buses among wheeled mobility device users suggests the need to identify vehicle design conditions that are either particularly accommodating or challenging. The objective of this study was to determine the effects of low-floor bus interior seating configuration and passenger load on wheeled mobility device user-reported difficulty, overall acceptability and design preference.

METHODS

Forty-eight wheeled mobility users evaluated three interior design layouts at two levels of passenger load (high vs. low) after simulating boarding and disembarking tasks on a static full-scale low-floor bus mockup.

RESULTS

User self-reports of task difficulty, acceptability and design preference were analyzed across the different test conditions. Ramp ascent was the most difficult task for manual wheelchair users relative to other tasks. The most difficult tasks for users of power wheelchairs and scooters were related to interior circulation, including moving to the securement area, entry and positioning in the securement area and exiting the securement area. Boarding and disembarking at the rear doorway was significantly more acceptable and preferred compared to the layouts with front doorways.

CONCLUSION

Understanding transit usability barriers, perceptions and preferences among wheeled mobility users is an important consideration for clinicians who recommend mobility-related device interventions to those who use public transportation. Implications for Rehabilitation In order to maximize community participation opportunities for wheeled mobility users, clinicians should consider potential public transit barriers during the processes of wheelchair device selection and skills training. Usability barriers experienced by wheeled mobility device users on transit vehicles differ by mobility device type and vehicle configurations. Full-scale environment simulations are an effective means of identifying usability barriers and design needs in people with mobility impairments and may provide an alternative model for determining readiness for using fixed route buses or eligibility for paratransit.

USEFULNESS OF GASTRIC SUBMUCOSAL DISSECTION DEPTH TO EVALUATE SKILL ACQUIREMENT IN SHORT TERM TRAINING COURSES IN ESD: AN EXPERIMENTAL STUDY

BACKGROUND

Endoscopic submucosal dissection (ESD) is a complex endoscopic procedure, with high rates of adverse events and technical difficulties. To overcome that problem, many training centers published the importance of animal models for skill acquirement in ESD. However, no study has used the submucosal dissection depth (DSUB) as a parameter to evaluate the learning curve in ESD, which might be a relevant factor since an optimal resection plane is important to achieve a curative resection and avoid intraoperative complications.

OBJECTIVE

This study aimed to assess ESD skill acquirement after short-term training sessions by evaluating the submucosal dissection depth (DSUB) and the association with adverse events.

METHODS

This experimental study included 25 experienced endoscopists in therapeuthic procedures (>5years) and 75 specimens resected by ESD (three resections / endoscopist). Learning parameters (resection time, size, en bloc resection rate, bleeding, perforation and submucosal dissection depth) were prospectively evaluated. The percentages of DSUB of all specimens resected were calculated.

RESULTS

All specimens were resected from the gastric body (n=75). The mean size of the resected specimens was 23.97±7.2 mm. The number of adverse events, including bleeding, perforation, and death, were 17 (22.67%), 3 (4%), and 0 cases, respectively. The average mean time by the third dissection decreased from 28.44±9.73 to 18.72±8.81 min (P<0.001). The proportion of DSUB in the bleeding and non-bleeding group were respectively 37.97%±21.13% and 68.66%±23.99%, indicating a significant association between DSUB and bleeding incidence (P<0.001). The ROC curve analysis indicated a cut-off point of 61% (sensitivity, 64%; specificity, 94%) of submucosal dissection depth associated with bleeding. Therefore, when ESD was performed at a depth of >61% of the submucosal layer, the risk for bleeding during the procedure decreased (PPV, 0.97; 95% CI, 0.85-0.99).

CONCLUSION

Improvement in the learning curve in ESD and a better cognitive ability were seen by the third dissection in these short term training courses. And a significant association between DSUB and the risk of bleeding.

Vedolizumab use after failure of TNF-α antagonists in children and adolescents with inflammatory bowel disease

BACKGROUND

Vedolizumab is safe and effective in adult patients with Crohn's disease (CD) and ulcerative colitis (UC); however, data in children with inflammatory bowel disease (IBD) are scarce. Therefore, we evaluated vedolizumab use in a cohort of Austrian paediatric patients with IBD.

METHODS

Twelve patients (7 female; 7 CD; 5 UC), aged 8-17 years (median, 15 years), with severe IBD who received vedolizumab after tumour necrosis factor α antagonist treatment were retrospectively analysed. Clinical activity scores, relevant laboratory parameters, and auxological measures were obtained at infusion visits.

RESULTS

In the CD group, 1/7 patient discontinued therapy due to a severe systemic allergic reaction; 1/7 and 2/7 patients achieved complete and partial response, respectively, at week 14; and 3/7 patients discontinued therapy due to a primary non-response or loss of response. In the UC group, complete clinical remission was achieved at weeks 2, 6, and 14 in 2/5, 1/5 and 1/5 patients respectively; partial response was observed in one patient at week 2. CD activity scores did not significantly change from baseline to week 38 (median 47.5 vs. 40 points, p = 1,0), while median UC activity scores changed from 70 to 5 points (p < 0,001). Substantial weight gain and increased albumin and haemoglobin levels were observed in both groups.

CONCLUSION

These results demonstrate that vedolizumab can be an effective treatment for individual paediatric patients with IBD who are unresponsive, intolerant, or experience a loss of efficacy in other therapies. However, vedolizumab appears to be more effective in paediatric UC than in paediatric CD.

Effects of transit bus interior configuration on performance of wheeled mobility users during simulated boarding and disembarking

The emergence of low-floor bus designs and related regulatory standards in the U.S. have resulted in substantial improvements in public transit accessibility. However, passengers using wheeled mobility devices still experience safety concerns and inefficiencies in boarding, disembarking, and interior circulation on low-floor buses. This study investigates effects of low-floor bus interior configuration and passenger crowding on boarding and disembarking efficiency and safety. Users of manual wheelchairs (n = 18), powered wheelchairs (n = 21) and electric scooters (n = 9) simulated boarding and disembarking in three interior layout configurations at low and high passenger crowding conditions on a full-scale laboratory mock-up of a low-floor bus. Dependent measures comprised task times and critical incidents during access ramp use, fare payment, and movement to and from the doorway and wheeled mobility securement area. Individual times for unassisted boarding ranged from 15.2 to 245.3 s and for disembarking ranged from 9.1 to 164.6 s across layout and passenger crowding conditions. Nonparametric analysis of variance showed significant differences and interactions across vehicle design conditions, passenger load and mobility device type on user performance. The configuration having electronic on-board fare payment, rear-bus entrance doorways and adjacent device securement areas demonstrated greatest efficiency and safety. High passenger load adversely impacted efficiency and frequency of critical incidents during on-board circulation across all three layouts. Findings have broader implications for improving transit system efficiency and quality of service across the spectrum of transit users.

A novel rank-based non-parametric method for longitudinal ordinal data

Longitudinal ordinal data are common in biomedical research. Although various methods for the analysis of such data have been proposed in the past few decades, they are limited in several ways. For instance, the constraints on parameters in the proportional odds model may result in convergence problems; the rank-based aligned rank transform method imposes constraints on other parameters and the distributional assumptions with parametric model. We propose a novel rank-based non-parametric method that models the profile rather than the distribution of the data to make an effective statistical inference without the constraint conditions. We construct the test statistic of the interaction first, and then construct the test statistics of the main effects separately with or without the interaction, while "adjusted coefficient" for the case of ties is derived. A simulation study is conducted for comparison between rank-based non-parametric and rank-transformed analysis of variance. The results show that type I errors of the two methods are both maintained closer to the priori level, but the statistical power of rank-based non-parametric is greater than that of rank-transformed analysis of variance, suggesting higher efficiency of the former. We then apply rank-based non-parametric to two real studies on acne and osteoporosis, and the results also illustrate the effectiveness of rank-based non-parametric, particularly when the distribution is skewed.

Myocardial blood flow assessment with 82rubidium-PET imaging in patients with left bundle branch block

OBJECTIVES

Perfusion abnormalities are frequently seen in Single Photon Emission Computed Tomography (SPECT) when a left bundle branch block is present. A few studies have shown decreased coronary flow reserve in the left anterior descending territory, regardless of the presence of coronary artery disease.

OBJECTIVE

We sought to investigate rubidium-82 (82Rb) positron emission tomography imaging in the assessment of myocardial blood flow and coronary flow reserve in patients with left bundle branch block.

METHODS

Thirty-eight patients with left bundle branch block (GI), median age 63.5 years, 22 (58%) female, 12 with coronary artery disease (≥70%; GI-A) and 26 with no evidence of significant coronary artery disease (GI-B), underwent rest-dipyridamole stress 82Rb-positron emission tomography with absolute quantitative flow measurements using Cedars-Sinai software (mL/min/g). The relative myocardial perfusion and left ventricular ejection fraction were assessed in 17 segments. These parameters were compared with those obtained from 30 patients with normal 82Rb-positron emission tomography studies and without left bundle branch block (GII).

RESULTS

Stress myocardial blood flow and coronary flow reserve were significantly lower in GI than in GII (p<0.05). The comparison of coronary flow reserve between GI-A and GI-B showed that it was different from the global coronary flow reserve (p<0.05) and the stress flow was significantly lower in the anterior than in the septal wall for both groups. Perfusion abnormalities were more prevalent in GI-A (p=0.06) and the left ventricular ejection fraction was not different between GI-A and GI-B, whereas it was lower in GI than in GII (p<0.001).

CONCLUSION

The data confirm that patients with left bundle branch block had decreased myocardial blood flow and coronary flow reserve and coronary flow reserve assessed by 82Rb-positron emission tomography imaging may be useful in identifying coronary artery disease in patients with left bundle branch block.

Simultaneous comparisons of treatments at multiple time points: Combined marginal models versus joint modeling

We discuss several aspects of multiple inference in longitudinal settings, focusing on many-to-one and all-pairwise comparisons of (a) treatment groups simultaneously at several points in time, or (b) time points simultaneously for several treatments. We assume a continuous endpoint that is measured repeatedly over time and contrast two basic modeling strategies: fitting a joint model across all occasions (with random effects and/or some residual covariance structure to account for heteroscedasticity and serial dependence), and a novel approach combining a set of simple marginal, i.e. occasion-specific models. Upon parameter and covariance estimation with either modeling approach, we employ a variant of multiple contrast tests that acknowledges correlation between time points and test statistics. This method provides simultaneous confidence intervals and adjusted p-values for elementary hypotheses as well as a global test decision. We compare via simulation the powers of multiple contrast tests based on a joint model and multiple marginal models, respectively, and quantify the benefit of incorporating longitudinal correlation, i.e. the advantage over Bonferroni. Practical application is illustrated with data from a clinical trial on bradykinin receptor antagonism.