Mathematical coupling may account for the association between baseline severity and minimally important difference values

Should We Wait for Bone-on-Bone Arthritis? Equivalent Clinical Outcomes in Patients Requiring Advanced Imaging Prior to Primary Total Hip Arthroplasty

INTRODUCTION

Plain radiographs remain the standard for diagnosing osteoarthritis (OA). Total hip arthroplasty (THA) is generally offered only for advanced OA by plain radiographs. Advanced imaging is used as an adjunct to assess OA severity in cases of progressive symptoms with less advanced OA by plain radiographs. The objective of this study was to compare outcomes following THA in patients who have advanced OA visualized by plain radiographs to patients who have less severe OA visualized by plain radiographs.

METHODS

From February 2016 to February 2020, 93 patients who had Kellgren-Lawrence (KL) grade 0 to 2 OA and underwent THA were identified. The median age was 65 years, and 55% were women. They were matched 1:3 to patients who underwent THA for KL 4 OA based on age, sex, BMI, and Charlson Comorbidity Index. The primary outcome was achievement of the Hip Injury and Osteoarthritis Outcome Score, Joint Replacement (HOOS JR) minimum clinically important difference (MCID), substantial clinical benefit (SCB), and patient acceptable symptom state (PASS) at 1 year postoperatively.

RESULTS

There was no difference between the KL 0 to 2 and KL 4 cohorts in the achievement of HOOS JR MCID (86 versus 85.6%, P = 0.922), SCB (81.7 versus 80.2%, P = 0.751), or PASS (89.2 versus 85.6%, P = 0.374). The KL 0 to 2 cohort had a similar improvement in their 2-year HOOS JR (42.5 versus 38.6, P = 0.019).

CONCLUSION

In this series, there was no difference in outcomes following primary THA between patients who have severe OA on plain radiographs (KL 4) compared to those who have less severe OA (KL 0 to 2). In the setting of severe symptoms and the absence of advanced OA on radiographs, advanced imaging can be used to guide treatment and select patients who could benefit from THA.

Rate-dependent effects of narrative interventions in a longitudinal study of individuals who use alcohol

BACKGROUND

Delay discounting (DD), the decrease in reward valuation as a function of delay to receipt, is a key process undergirding alcohol use. Narrative interventions, including episodic future thinking (EFT), have decreased delay discounting and demand for alcohol. Rate dependence, the relationship between a baseline rate and change in that rate after an intervention, has been evidenced as a marker of efficacious substance use treatment, but whether narrative interventions have rate-dependent effects needs to be better understood. We investigated the effects of narrative interventions on delay discounting and hypothetical demand for alcohol in this longitudinal, online study.

METHODS

Individuals (n = 696) reporting high- or low-risk alcohol use were recruited for a longitudinal 3-week survey via Amazon Mechanical Turk. Delay discounting and alcohol demand breakpoint were assessed at baseline. Individuals returned at weeks 2 and 3 and were randomized into the EFT or scarcity narrative interventions and again completed the delay discounting tasks and alcohol breakpoint task. Oldham's correlation was used to explore the rate-dependent effects of narrative interventions. Study attrition as a function of delay discounting was assessed.

RESULTS

Episodic future thinking significantly decreased, while scarcity significantly increased delay discounting relative to baseline. No effects of EFT or scarcity on the alcohol demand breakpoint were observed. Significant rate-dependent effects were observed for both narrative intervention types. Higher delay discounting rates were associated with a greater likelihood of attrition from the study.

CONCLUSION

The evidence of a rate-dependent effect of EFT on delay discounting rates offers a more nuanced, mechanistic understanding of this novel therapeutic intervention and can allow more precise treatment targeting by demonstrating who is likely to receive the most benefit from it.

Mepolizumab improvements in health-related quality of life and disease symptoms in a patient population with very severe chronic rhinosinusitis with nasal polyps: psychometric and efficacy analyses from the SYNAPSE study

BACKGROUND

Although the psychometric properties of patient-reported outcome measures (e.g. the 22-item Sino-nasal Outcomes Test [SNOT-22]) in chronic rhinosinusitis with nasal polyps (CRSwNP) have been defined, these definitions have not been extensively studied in patients with very severe CRSwNP, as defined by recurrent disease despite ≥ 1 previous surgery and a current need for further surgery. Therefore, the psychometric properties of the symptoms visual analogue scales (VAS) were evaluated, and meaningful within-patient change thresholds were calculated for VAS and SNOT-22.

METHODS

SYNAPSE (NCT03085797), a randomized, double-blind, placebo-controlled, 52-week trial, assessed the efficacy and safety of 4-weekly mepolizumab 100 mg subcutaneously added to standard of care in very severe CRSwNP. Enrolled patients (n = 407) completed symptom VAS (six items) daily and SNOT-22 every 4 weeks from baseline until Week 52. Blinded psychometric assessment of individual and composite VAS was performed post hoc, including anchor-based thresholds for meaningful within-patient changes for VAS and SNOT-22, supported by cumulative distribution function and probability density function plots. The effect of mepolizumab versus placebo for 52 weeks on VAS and SNOT-22 scores was then determined using these thresholds using unblinded data.

RESULTS

Internal consistency was acceptable for VAS and SNOT-22 scores (Cronbach's α-coefficients ≥ 0.70). Test-retest reliability was demonstrated for all symptom VAS (Intra-Class Correlation coefficients > 0.75). Construct validity was acceptable between individual and composite VAS and SNOT-22 total score (r = 0.461-0.598) and between individual symptom VAS and corresponding SNOT-22 items (r = 0.560-0.780), based upon pre-specified ranges. Known-groups validity assessment demonstrated generally acceptable validity based on factors associated with respiratory health, with all VAS responsive to change. Mepolizumab treatment was associated with significantly increased odds of meeting or exceeding meaningful within-patient change thresholds, derived for this very severe cohort using six anchor groups for individual VAS (odds ratio [OR] 2.19-2.68) at Weeks 49-52, and SNOT-22 (OR 1.61-2.96) throughout the study.

CONCLUSIONS

Symptoms VAS and SNOT-22 had acceptable psychometric properties for use in very severe CRSwNP. Mepolizumab provided meaningful within-patient improvements in symptom severity and health-related quality of life versus placebo, indicating mepolizumab provides substantial clinical benefits in very severe CRSwNP.

Estimating Clinically Meaningful Change of Efficacy Outcomes in Inadequately Controlled Chronic Rhinosinusitis with Nasal Polyposis

OBJECTIVES/HYPOTHESIS

Clinical trials of biologics to treat chronic rhinosinusitis with nasal polyposis (CRSwNP) have evaluated objective outcomes (e.g., University of Pennsylvania Smell Identification Test [UPSIT], nasal polyps score [NPS], and computed tomography Lund-Mackay score [CT-LMK]) and patient-reported symptoms (e.g., nasal congestion/obstruction [NC], loss of smell [LoS], and total symptom score [TSS]). We estimated anchor-based thresholds for clinically meaningful change in objective and patient-reported outcomes in patients with CRSwNP using data from LIBERTY NP SINUS-24 and SINUS-52 trials (NCT02912468; NCT02898454).

METHODS

Target patient-reported outcomes were NC, LoS, and TSS; target objective outcomes were UPSIT, NPS, and CT-LMK. Anchor measures were the 22-item sinonasal outcome test (SNOT-22) rhinologic symptoms domain and total score and rhinosinusitis visual analog scale (VAS). The appropriateness of each anchor measure was evaluated by reviewing correlations between change in anchor measures and target outcomes and descriptive scores on target outcomes by levels of change in the anchor measure. Established thresholds for anchor measures (3.8 points for SNOT-22 rhinologic symptoms, 8.9 points for SNOT-22 total, 1-category improvement for rhinosinusitis VAS) were used to estimate clinically meaningful score changes for each target outcome.

RESULTS

Based on correlations between change in anchor measures and target outcomes, SNOT-22 rhinologic symptoms domain was deemed the most appropriate anchor measure. Using this anchor measure, thresholds for clinically meaningful within-patient change were NC: 1 point; LoS: 1 point; TSS: 3 points; UPSIT: 8 points; NPS: 1 point; and CT-LMK: 5 points.

CONCLUSION

These thresholds support interpretation of efficacy results for target outcomes in CRSwNP trials.

LEVEL OF EVIDENCE

2 Laryngoscope, 2021.

Statistical Considerations for Drawing Conclusions About Recovery

BACKGROUND

Numerous studies have found associations when change scores are regressed onto initial impairments in people with stroke (slopes ≈ 0.7). However, there are important statistical considerations that limit the conclusions we can draw about recovery from these studies.

OBJECTIVE

To provide an accessible checklist of conceptual and analytical issues on longitudinal measures of stroke recovery. Proportional recovery is an illustrative example, but these considerations apply broadly to studies of change over time.

METHODS

Using a pooled data set of n = 373 Fugl-Meyer Assessment upper extremity scores, we ran simulations to illustrate 3 considerations: (1) how change scores can be problematic in this context; (2) how "nil" and nonzero null-hypothesis significance tests can be used; and (3) how scale boundaries can create the illusion of proportionality, whereas other analytical procedures (eg, post hoc classifications) can augment this problem.

RESULTS

Our simulations highlight several limitations of common methods for analyzing recovery. We find that uniform recovery leads to similar group-level statistics (regression slopes) and individual-level classifications (into fitters and nonfitters) that have been claimed as evidence for the proportional recovery rule. New analyses, however, also speak to the complexities in variance about the regression slope.

CONCLUSIONS

Our results highlight that one cannot identify whether proportional recovery is true or not based on commonly used methods. We illustrate how these techniques, measurement tools, and post hoc classifications (eg, nonfitters) can create spurious results. Going forward, the field needs to carefully consider the influence of these factors on how we measure, analyze, and conceptualize recovery.

Methylmercury, attention, and memory: baseline-dependent effects of adult d-amphetamine and marginal effects of adolescent methylmercury

Methylmercury (MeHg) is an environmental neurotoxicant known to disrupt behavior related to dopamine neurotransmission in experimental models. Such disruptions are sensitive to dopamine agonists when administered acutely after exposure to MeHg has ended or when administered concurrently with MeHg exposure. Sustained attention and short-term remembering, components of attention-deficit/hyperactivity disorder (ADHD), are partially mediated by dopamine neurotransmission. In order to observe MeHg-related alterations in sustained attention and short-term memory, as well as determine sensitivity of MeHg exposed animals to dopamine agonists commonly used in the treatment of ADHD symptoms, rats were exposed to 0, 0.5, or 5 ppm MeHg throughout adolescence and trained in a hybrid sustained attention/short term memory visual signal detection task in adulthood. Behavior was then probed with acute i.p. injections of the dopamine agonist, d-amphetamine, which improves impaired attention and inhibits short-term memory in clinical syndromes like ADHD. Acute d-amphetamine dose-dependently decreased short-term memory as well as sustained attention. While MeHg alone did not impair accuracy or memory, it did interact with d-amphetamine to produce baseline-dependent inhibition of behavior. These findings further show that changes in behavior following low-level exposure to MeHg during adolescence are augmented by dopamine agonists. Observed impairments in memory following acute d-amphetamine are consistent with previous findings.

What Are the Minimal and Substantial Improvements in the HOOS and KOOS and JR Versions After Total Joint Replacement?

BACKGROUND

Patient-reported outcome measures (PROMs) are a gold standard for measuring therapeutic outcomes in research. Extending their use to inform clinical care decisions, determine the appropriateness of therapeutic choices, and assess healthcare quality is attractive but will require our professional community to establish valid estimates of minimal and substantial clinical improvements.

QUESTIONS/PURPOSES

The purposes of this study were (1) to assess the validity of estimates for the minimal clinically important difference (MCID) calculated using distribution- and anchor-based methods by determining whether they exceed the minimal detectable change (MDC) for the Hip Disability and Osteoarthritis Outcome Score (HOOS) and the Knee Injury and Osteoarthritis Outcome Score (KOOS) domains, the HOOS, joint replacement (JR) and the KOOS, JR among patients who underwent THA or TKA; (2) to determine substantial clinical benefit thresholds for the HOOS and KOOS domains, the HOOS, JR, and the KOOS, JR among patients who underwent THA or TKA; and (3) to assess the proportions of patients who underwent THA or TKA who achieved an MCID for the HOOS and KOOS domains, HOOS, JR, and KOOS, JR based on distribution-based and anchor-based methods as well as the percentages of patients who achieved substantial clinical benefit using the anchor-based method.

METHODS

Medicare patients enrolled in our institutional joint replacement registry who subsequently underwent THA (n = 2323) or TKA (n = 2630) between 2007 and 2012 completed HOOS or KOOS preoperatively and 2 years postoperatively. Short-form joint replacement (JR) versions of each PROM were derived from the full PROMs. Of all eligible patients, 78% (3161 of 4080) of THAs and 74% of TKAs (3815 of 5156) consented to join the registry and completed a baseline survey, 88% (2796 of 3161) of THAs and 85% (3230 of 3815) of TKAs were eligible for followup survey administration, and 83% of THAs (2323 of 2796) and 81% (2630 of 3230) of TKAs returned 2-year surveys. For each HOOS domain, KOOS domain, HOOS, JR, and KOOS, JR, we calculated the calibration variation of the instrument (MDC) with confidence intervals (CIs) reflecting 80% (MDC80), 90% (MDC90), and 95% (MDC95) certainty; we calculated the smallest difference joint health patients might detect (MCID) using distribution- and anchor-based approaches and the difference that can be considered a large improvement in joint health (substantial clinical benefit) using an anchor-based approach.

RESULTS

Patients undergoing THA were 57% female with a mean (± SD) age of 73 ± 6 years, whereas patients undergoing TKA were 63% female with a mean age of 74 ± 6 years. Depending on the CI chosen for the MDC, values ranged from 7 to 16 for the HOOS and KOOS domains and the JRs. The MCIDs ranged from 6 to 9 for the distribution-based approach and 7 to 36 for the anchor-based approach. All HOOS and KOOS domains and all JR scores are scores from 0 (worst joint health) to 100 (best joint health). The MCIDs calculated using the distribution-based approach were not valid, because they were lower than the MDC for all HOOS/KOOS domains and both JRs at every confidence level. The anchor-based receiver operating characteristic approach, on the other hand, resulted in MCIDs exceeding MDC80 for seven of eight HOOS/KOOS domains and MDC95 for both JR scores. For all domains and JR versions, substantial clinical benefits ranged from 15 to 36, exceeding MDC95 in all domains and JR scores. Across HOOS and KOOS domains as well as the JR, the proportion of patients undergoing THA who achieved an MCID ranged from 77% to 95% with the distribution-based method and from 67% to 96% using the anchor-based method. The proportion achieving substantial clinical benefit ranged from 67% to 85%.

CONCLUSIONS

The MDC and MCID differ greatly based on assumptions and methods used. The MCID anchor-based approach had superior construct and face validity compared with the MCID distribution-based approach, which never exceeded even small MDCs. Achieving consensus about standard definitions of meaningful improvement will be necessary to maximize utility of these PROMs to inform clinical care or performance measurement.

LEVEL OF EVIDENCE

Level III, diagnostic study.

The Discord Outcome Analysis (DOA) as a Reporting Standard at Three Months and Five Years in Randomised Varicose Vein Treatment Trials

OBJECTIVES

Treatment success for chronic superficial venous insufficiency could be defined as an improvement in three domains: (i) disease specific quality of life, (ii) clinical severity, (iii) reflux. The aim was to report these at five years using a Venn diagram to profile the outcomes: a discord outcome analysis (DOA).

METHODS

Patients (n = 50 patients/legs in each treated group) were randomised to endovenous laser ablation (EVLA) with concurrent phlebectomies vs. ultrasound guided foam sclerotherapy (UGFS). Outcomes were assessed using three domains: (i) Aberdeen varicose vein questionnaire (AVVQ), (ii) venous clinical severity score (VCSS), (iii) venous filling index (VFI) of air plethysmography. Change scores were calculated by subtracting the final score after treatment from the baseline score before treatment to quantify the improvement. This was followed by a DOA profile for each patient where a discord was defined as the percentage of patients with a numerical deterioration in one or two domains.

RESULTS

The median [interquartile range] follow up was 68 [64-72] months. Follow up in all three domains was EVLA: 45/50, UGFS: 42/50. On ultrasound examination, GSV occlusion at some point above the knee was 93% for EVLA and 64% for UGFS (p = .001). There was no significant difference in improvement between the two treatment groups in the VCSS and the VFI. However, the EVLA group had a statistically significant AVVQ improvement (p = .004). Using a DOA, only 76% EVLA versus 60% UGFS had success in all three domains. Using improvement thresholds, this reduced to 54% and 39%, respectively. The commonest discord pattern was an improvement in the VCSS and VFI but deterioration in the AVVQ.

CONCLUSIONS

A DOA demonstrated that the definition of success is reduced if deterioration in one or two domains is taken into account. A DOA should be considered as a reporting standard for comparative analyses.

Working Memory Training Improves Alcohol Users' Episodic Future Thinking: A Rate-Dependent Analysis

BACKGROUND

Episodic thinking, whether past or future, uses similar neural machinery, and individuals with alcohol dependence have clear challenges with both. Moreover, alcohol-dependent individuals' narrowed temporal window likely gives rise to greater valuation of immediate rewards. We aimed to strengthen working memory (WM) in alcohol-dependent individuals and measure performance on near-transfer (novel WM) and far-transfer delay discounting (DD) tasks, including episodic future thinking (EFT) performance. Importantly, heterogeneous intervention responses could obscure a treatment effect due to individuals' baseline differences. Therefore, we considered WM, DD, and EFT DD scores using rate-dependent analyses.

METHODS

A total of 50 alcohol-dependent individuals received either 20 active (Trained) or sham (Control) WM training sessions using the Cogmed adaptive WM training program. Participants completed a near-transfer novel WM task and far-transfer DD and EFT DD tasks before and after training.

RESULTS

Active WM training improved performance on the near-transfer task. As determined by Oldham's correlation [r_{mean(x,y),y-x}], initially low near-transfer task scores improved more than initially high scores (i.e., rate dependence) in the Trained group only. Moreover, Trained group individuals with the highest rates of EFT DD at baseline rate-dependently decreased following training, whereas WM training had no effect on DD alone.

CONCLUSIONS

These data support the notion that WM training improves near-transfer task performance and may enhance the effects of EFT DD in a subset of alcohol-dependent individuals trapped within the narrowest temporal window. Rate-dependent changes highlight that we should attend to baseline performance to better identify individuals who would most benefit from an intervention.

Reductions in Readmission Rates Are Associated With Modest Improvements in Patient-reported Health Gains Following Hip and Knee Replacement in England

Supplemental Digital Content is available in the text.

Background:

Although many hospital readmission reduction initiatives have been introduced globally, health care systems ultimately aim to improve patients’ health and well-being. We examined whether the hospitals that report greater success in reducing readmissions also see greater improvements in patient-reported outcomes.

Research Design:

We examined hospital groups (Trusts) that provided hip replacement or knee replacement surgery in England between April 2010 and February 2013. For each Trust, we calculated risk-adjusted 30-day readmission rates from administrative datasets. We also obtained changes in patient-reported health between presurgical assessment and 6-month follow-up, using general health EuroQuol five dimensions questionaire (EQ-5D) and EuroQuol visual analogue scales (EQ-VAS) and procedure-specific (Oxford Hip and Knee Scores) measures. Panel models were used to assess whether changes over time in risk-adjusted readmission rates were associated with changes over time in risk-adjusted health gains.

Results:

Each percentage point reduction in the risk-adjusted readmission rate for hip replacement was associated with an additional health gain of 0.004 for EQ-5D [95% confidence interval (CI), 0.002–0.006], 0.39 for EQ-VAS (95% CI, 0.26–0.52), and 0.32 for Oxford Hip Score (95% CI, 0.15–0.27). Corresponding figures for knee replacement were 0.003 for EQ-5D (95% CI, 0.001–0.004), 0.21 for EQ-VAS (95% CI, 0.12–0.30), and 0.14 in the Oxford Knee Score (95% CI, 0.09–0.20).

Conclusions:

Reductions in readmission rates were associated with modest improvements in patients’ sense of their health and well-being at the hospital group level. In particular, fears that efforts to reduce readmission rates have had unintended consequences for patients appear to be unfounded.

Use of large-scale HRQoL datasets to generate individualised predictions and inform patients about the likely benefit of surgery

Purpose

The English NHS has mandated the routine collection of health-related quality of life (HRQoL) data before and after surgery, giving prospective patient information about the likely benefit of surgery. Yet, the information is difficult to access and interpret because it is not presented in a lay-friendly format and does not reflect patients’ individual circumstances. We set out a methodology to generate personalised information to help patients make informed decisions.

Methods

We used anonymised, pre- and postoperative EuroQol-5D-3L (EQ-5D) data for over 490,000 English NHS patients who underwent primary hip or knee replacement surgery or groin hernia repair between April 2009 and March 2016. We estimated linear regression models to relate changes in EQ-5D utility scores to patients’ own assessment of the success of surgery, and calculated from that minimally important differences for health improvements/deteriorations. Classification tree analysis was used to develop algorithms that sort patients into homogeneous groups that best predict postoperative EQ-5D utility scores.

Results

Patients were classified into between 55 (hip replacement) to 60 (hernia repair) homogeneous groups. The classifications explained between 14 and 27% of variation in postoperative EQ-5D utility score.

Conclusions

Patients are heterogeneous in their expected benefit from surgery, and decision aids should reflect this. Large administrative datasets on HRQoL can be used to generate the required individualised predictions to inform patients.

Application of minimal important differences in degenerative knee disease outcomes: a systematic review and case study to inform BMJ Rapid Recommendations

OBJECTIVES

To identify the most credible anchor-based minimal important differences (MIDs) for patient important outcomes in patients with degenerative knee disease, and to inform BMJ Rapid Recommendations for arthroscopic surgery versus conservative management DESIGN: Systematic review.

OUTCOME MEASURES

Estimates of anchor-based MIDs, and their credibility, for knee symptoms and health-related quality of life (HRQoL).

DATA SOURCES

MEDLINE, EMBASE and PsycINFO.

ELIGIBILITY CRITERIA

We included original studies documenting the development of anchor-based MIDs for patient-reported outcomes (PROs) reported in randomised controlled trials included in the linked systematic review and meta-analysis and judged by the parallel BMJ Rapid Recommendations panel as critically important for informing their recommendation: measures of pain, function and HRQoL.

RESULTS

13 studies reported 95 empirically estimated anchor-based MIDs for 8 PRO instruments and/or their subdomains that measure knee pain, function or HRQoL. All studies used a transition rating (global rating of change) as the anchor to ascertain the MID. Among PROs with more than 1 estimated MID, we found wide variation in MID values. Many studies suffered from serious methodological limitations. We identified the following most credible MIDs: Western Ontario and McMaster University Osteoarthritis Index (WOMAC; pain: 12, function: 13), Knee injury and Osteoarthritis Outcome Score (KOOS; pain: 12, activities of daily living: 8) and EuroQol five dimensions Questionnaire (EQ-5D; 0.15).

CONCLUSIONS

We were able to distinguish between more and less credible MID estimates and provide best estimates for key instruments that informed evidence presentation in the associated systematic review and judgements made by the Rapid Recommendation panel.

TRIAL REGISTRATION NUMBER

CRD42016047912.

Patient-reported health outcomes after total hip and knee surgery in a Dutch University Hospital Setting: results of twenty years clinical registry

Background

Patient-Reported Outcome (PRO) measurement is a method for measuring perceptions of patients on their health and quality of life. The aim of this paper is to present the results of PRO measurements in total hip and knee replacement as routinely collected during 20 years of surgery in a university hospital setting.

Methods

Data of consecutive patients between 1993 and 2014 were collected. Health outcomes were measured pre-surgery and at 3, 6, and 12 months post-surgery. Outcomes for hip replacement were measured with the Harris Hip Score (HHS) and Oxford Hip Score (OHS). Outcomes for knee replacement were measured with the Western Ontario and McMaster Universities Arthritis Index (WOMAC) and the Knee Society Score (KSS). A Visual Analog Scale (VAS) for pain was used. Absolute and relative Minimal Clinically Important Differences (MCID) were estimated. Generalized estimating equation analysis was used for estimating mean outcomes. Trends over time were analyzed.

Results

The database contained 2,089 patients with hip replacement, and 704 patients with knee replacement. Mean HHS and OHS scores in primary hip replacement at 12 months post-surgery were 86.7 (SD: 14.5) and 41.1 (SD: 7.5) respectively. Improvements on the HHS based on absolute MCID was lower for revisions compared to primary hip replacements, with 72.4% and 87.0% respectively. Mean WOMAC and KSS scores in knee replacement at 12 months post-surgery were 21.5 (SD: 18.2) and 67.0 (SD: 26.4) respectively. Improvements based on absolute MCID were lowest for the KSS (62.6%) and highest for VAS pain (85.6%). Trend analysis showed a difference in 1 out of 24 comparisons in hip replacement and in 2 out of 9 comparisons in knee replacement.

Conclusions

The functional status of a large cohort of patients significantly improved after hip and knee replacement based on routine data collection. Our study shows the feasibility of the routine collection of PRO data in patients with total hip and knee replacement. The use of PRO data provides opportunities for continuous quality improvement.

The misleading concept of initial severity in depression clinical trials: development and results from a mathematical model

OBJECTIVE

Recently, meta-analytic studies have suggested a positive relationship between initial severity and magnitude of treatment efficacy. The aim of the current study was to develop a mathematical model to test the assumption concerning the role of initial severity in treatment response.

METHODS

A number of experimental artificial datasets were developed on the basis of three different scenarios which reflect a pre-determined effect of initial severity. They were used to test for correlations at the patient level as well as at the meta-analysis level (trial level).

RESULTS

The results suggested that in all scenarios and analyses the correlations were so high that a ceiling effect was obvious. The testing concerned changes from baseline, but not differences between arms.

CONCLUSIONS

Overall the data suggest that the question concerning the role of initial severity cannot be answered. Any allegations on such a role are based on flawed methodology and do not take into consideration the true nature of data.

The Return of Rate Dependence

Rate dependence, a well-known phenomenon in behavioral pharmacology, appears to have declined as a topic of interest, perhaps, as a result of being viewed pertinent to only the preclinical investigation of drugs on schedule-controlled performance. Obstacles to data interpretation due to conflation with regression to the mean also appear to have contributed to the topic's decline. Despite this reduction in exposure, rate dependence is a useful concept and tool that can be used to determine sources of variability, predict therapeutic outcomes, and identify individuals that are most likely to respond therapeutically. Armed with new statistical methods and an understanding of the broad range of conditions under which rate dependence can be observed, we urge researchers to revisit the concept, use the appropriate analysis methods, and to design empirical studies a priori to further explore rate dependence.

Order in the absence of an effect: Identifying rate-dependent relationships

The heterogeneity of group data can obscure a significant effect of an intervention due to differential baseline scores. Instead of discarding the seemingly heterogeneous response set, an orderly lawful relationship could be present. Rate dependence describes a pattern between a baseline and the change in that baseline following some intervention. To highlight the importance of analyzing data from a rate-dependent perspective, we (1) briefly review research illustrating that rate-dependent effects can be observed in response to both drug and non-drug interventions in varied schedules of reinforcement in clinical and preclinical populations; (2) observe that the process of rate-dependence likely requires multiple parts of a system operating simultaneously to evoke differential responding as a function of baseline; and (3) describe several statistical methods for consideration and posit that Oldham's correlation is the most appropriate for rate-dependent analyses. Finally, we propose future applications for these analyses in which the level of baseline behavior exhibited prior to an intervention may determine the magnitude and direction of behavior change and can lead to the identification of subpopulations that would be benefitted. In sum, rate dependence is an invaluable perspective to examine data following any intervention in order to identify previously overlooked results.

Does impulsivity change rate dependently following stimulant administration? A translational selective review and re-analysis

RATIONALE

Rate dependence refers to an orderly relationship between a baseline measure of behavior and the change in that behavior following an intervention. The most frequently observed rate-dependent effect is an inverse relationship between the baseline rate of behavior and response rates following an intervention. A previous report of rate dependence in delay discounting suggests that the discounting of delayed reinforcers, and perhaps, other impulsivity measures, may change rate dependently following acute and chronic administration of potentially therapeutic medications in both preclinical and clinical studies.

OBJECTIVE

The aim of the current paper was to review the effects of stimulants on delay discounting and other impulsivity tasks.

METHODS

All studies identified from the literature were required to include (1) an objective measure of impulsivity; (2) administration of amphetamine, methylphenidate, or modafinil; (3) presentation of a pre- and postdrug administration impulsivity measure; and (4) the report of individual drug effects or results in groups split by baseline or vehicle impulsivity. Twenty-five research reports were then reanalyzed for evidence consistent with rate dependence.

RESULTS

Of the total possible instances, 67 % produced results consistent with rate dependence. Specifically, 72, 45, and 80 % of the data sets were consistent with rate dependence following amphetamine, methylphenidate, and modafinil administration, respectively.

CONCLUSIONS

These results suggest that rate dependence is a more robust phenomenon than reported in the literature. Impulsivity studies should consider this quantitative signature as a process to determine the effects of variables and as a potential prognostic tool to evaluate the effectiveness of future interventions.

Relationship between patient-reported outcomes of elective surgery and hospital and consultant volume

OBJECTIVE

Our aim was to analyze the relationship for 3 elective operations between outcome [patient-reported outcome measures (PROMs) for functional status, health-related quality of life, and postoperative complications] and both hospital and consultant volume.

METHODS

Hospitals (NHS and independent) and consultants undertaking at least 10 NHS-funded procedures during 2011/2012 were included (230 hospitals for hip and knee replacement, 257 for hernia repair; 978 consultants for hip replacement, 1172 for knee replacement, and 1288 for hernia repair). Outcomes (disease-specific and generic PROMs, patient-reported complications) were available from the NHS National PROMs Programme for 2009/2010 to 2011/2012. Relationship between case-mix adjusted outcomes and volume investigated using multilevel modeling.

RESULTS

There was considerable variation in hospital volumes (about 10-fold) and consultant volumes (about 5-fold). No significant association was observed between hospital volume and outcome for all 3 procedures. For consultant volume, there was no significant association for knee replacement or hernia repair. However, outcomes were statistically significantly better for hip replacement, although the effect was of little clinical significance: an additional 10 cases was associated with a higher Oxford Hip Score (0.06), higher EQ-5D score (0.001), and lower odds ratio of complications (0.992).

CONCLUSIONS

There are unlikely to be any benefits to patients from centralization of elective surgery into higher volume hospitals as regards the effectiveness of surgery or the avoidance of minor complications. There is some evidence that very low volume consultants achieve poorer outcomes than higher volume colleagues but the difference is slight and of little or no clinical significance.

Meaningful changes for the Oxford hip and knee scores after joint replacement surgery

Objectives

To present estimates of clinically meaningful or minimal important changes for the Oxford Hip Score (OHS) and the Oxford Knee Score (OKS) after joint replacement surgery.

Study Design and Setting

Secondary data analysis of the NHS patient-reported outcome measures data set that included 82,415 patients listed for hip replacement surgery and 94,015 patients listed for knee replacement surgery was performed.

Results

Anchor-based methods revealed that meaningful change indices at the group level [minimal important change (MIC)], for example in cohort studies, were ∼11 points for the OHS and ∼9 points for the OKS. For assessment of individual patients, receiver operating characteristic analysis produced MICs of 8 and 7 points for OHS and OKS, respectively. Additionally, the between group minimal important difference (MID), which allows the estimation of a clinically relevant difference in change scores from baseline when comparing two groups, that is, for clinical trials, was estimated to be ∼5 points for both the OKS and the OHS. The distribution-based minimal detectable change (MDC₉₀) estimates for the OKS and OHS were 4 and 5 points, respectively.

Conclusion

This study has produced and discussed estimates of minimal important change/difference for the OKS/OHS. These estimates should be used in the power calculations and the interpretation of studies using the OKS and OHS. The MDC₉₀ (∼4 points OKS and ∼5 points OHS) represents the smallest possible detectable change for each of these instruments, thus indicating that any lower value would fall within measurement error.

Individual patient monitoring in daily clinical practice: a critical evaluation of minimal important change

PURPOSE

In daily practice, physicians translate knowledge from clinical trials to practice, to improve health in individual patients. To help interpret meaningful change on disease outcome measures, the concept of minimal important change (MIC) was conceived. The objective of this study was to investigate whether MIC values are suited for individual patient monitoring.

METHODS

Three main elements of the MIC concept were evaluated: (1) MIC values for improvement and deterioration were determined, and the amount of misclassification present in quantifying minimal change was analyzed. (2) Discordance between change categories (improved, unchanged, deteriorated), defined by the MIC values, and patients' satisfaction with their health was inspected. (3) Discordance between change categories, defined by MIC values, and patients' willingness to alter therapy was inspected.

RESULTS

MIC value analysis was based on 469 patients with RA seen in daily practice. The chance of falsely classifying health change of an individual patient was high (false-positive range 19-30 % and false-negative range 43-72 %). Of patients classified as improved, 24 % were not satisfied with their health and 69 % were not willing to change therapy. Of patients classified as deteriorated, 54 % were satisfied with their health and 57 % were not willing to change therapy.

CONCLUSIONS

The misclassification in the quantification of change and high proportions of discordance between change categories defined by MIC cutoff values and patients' satisfaction and willingness to alter therapy indicate that MIC values as such are not suited for individual patient monitoring.

Dependence of the minimal clinically important improvement on the baseline value is a consequence of floor and ceiling effects and not different expectations by patients

OBJECTIVE

Estimates of minimal clinically important improvements (MCIIs) are larger among patients with higher values at baseline, suggesting that these patients require larger changes to appreciate improvements. We examined if baseline dependency of MCIIs was associated with specific patients across three measures, or was owing to floor and ceiling effects.

STUDY DESIGN AND SETTING

We prospectively examined 250 outpatients with active rheumatoid arthritis (RA). We used an anchor-based approach to estimate MCIIs for three measures of RA activity (patient global assessment, swollen joint count, and walking time). We examined if the same patients constituted the baseline subgroups with high MCIIs across measures.

RESULTS

The MCIIs were greater for those with higher baseline values of all three measures. At the ceiling, there was little opportunity to improve, and judgments were unrelated to measured changes. At midrange, improvements were balanced by worsenings, including some judged as improvements. At the floor, improvements were not similarly balanced. Patients in subgroups with high MCII for patient global assessment were not also predominantly in subgroups with high MCII for the swollen joint count or walking time, and vice versa.

CONCLUSION

Variation in MCII by baseline values is because of floor and ceiling effects rather than expectations of particular patients.

Patient acceptable symptom states after totalhip or knee replacement at mid-term follow-up: Thresholds of the Oxford hip and knee scores

Objectives

To define Patient Acceptable Symptom State (PASS) thresholds for the Oxford hip score (OHS) and Oxford knee score (OKS) at mid-term follow-up.

Methods

In a prospective multicentre cohort study, OHS and OKS were collected at a mean follow-up of three years (1.5 to 6.0), combined with a numeric rating scale (NRS) for satisfaction and an external validation question assessing the patient’s willingness to undergo surgery again. A total of 550 patients underwent total hip replacement (THR) and 367 underwent total knee replacement (TKR).

Results

Receiver operating characteristic (ROC) curves identified a PASS threshold of 42 for the OHS after THR and 37 for the OKS after TKR. THR patients with an OHS ≥ 42 and TKR patients with an OKS ≥ 37 had a higher NRS for satisfaction and a greater likelihood of being willing to undergo surgery again.

Conclusions

PASS thresholds appear larger at mid-term follow-up than at six months after surgery. With- out external validation, we would advise against using these PASS thresholds as absolute thresholds in defining whether or not a patient has attained an acceptable symptom state after THR or TKR.

Cite this article: Bone Joint Res 2014;3:7–13.

What is the optimal time point to assess patient-reported recovery after hip and knee replacement? A systematic review and analysis of routinely reported outcome data from the English patient-reported outcome measures programme

Background

It is unclear if there is a clinically important improvement in the six to 12-month recovery period after hip and knee replacement. This is an obvious gap in the evidence required by patients undergoing these procedures. It is also an issue for the English PROMs (Patient-Reported Outcome Measures) Programme which uses 6-month outcome data to compare the results of hospitals that perform hip and knee replacements.

Methods

A systematic review of studies reporting the Oxford Hip Score (OHS) or Oxford Knee Score (OKS) at 12 months after surgery was performed. This was compared with six-month outcome data collected for 60, 160 patients within the English PROMs programme. A minimally important difference of one standard error of the measurement, equivalent to 2.7 for the OHS and 2.1 for the OKS, was adopted.

Results and discussion

Six studies reported OHS data for 10 different groups containing 8,308 patients in total. In eight groups the change scores reported were at least 2.7 points higher than the six-month change observed in the PROMs programme (20.2 points). Nine studies reported OKS data for 13 different groups containing 4,369 patients in total. In eight groups the change scores reported were at least 2.1 points higher than the six-month change observed in the PROMs programme (15.0 points).

Conclusions

There is some evidence from this systematic review that clinically important improvement in the Oxford hip and knee scores occurs in the six to 12 month recovery period. This trend is more apparent for hip than knee replacement. Therefore we recommend that the English Department of Health study the impact on hospital comparisons of using 12- rather than six-month outcome data.

The Aberdeen Varicose Vein Questionnaire May be the Preferred Method of Rationing Patients for Varicose Vein Surgery

Rationing treatment of varicose veins (VVs) is of importance in countries with a public health service and limited funds. This study examines why and how the Aberdeen varicose vein questionnaire (AVVQ) can be used in achieving rationing. Baseline assessments prior to endovenous treatment included the venous clinical severity score (VCSS), venous filling index (VFI), and the refluxing great saphenous vein (GSV) diameter. Absolute change in the AVVQ defined improvement. There was no significant correlation in AVVQ improvement compared to baseline VCSS, VFI, GSV diameter or when patients were divided into mild and severe disease (C2,3 vs C4-6) or laser ablation versus foam sclerotherapy. However, AVVQ improvement significantly correlated at 3 weeks (n = 84) and 3 months (n = 70) with their baseline values ( r = .5 and r = .585), P < .0005 (Spearman). In conclusion, patients with an initial poor quality of life may benefit most from endovenous treatment, irrespective of other baseline severity assessments.

Clinicians' and patients' views of metrics of change derived from patient reported outcome measures (PROMs) for comparing providers' performance of surgery

BACKGROUND

Patient reported outcome measures (PROMs) are increasingly being used to compare the performance of health care providers. Our objectives were to determine the relative frequency of use of different metrics that can be derived from PROMs, explore clinicians' and patients' views of the options available, and make recommendations.

METHODS

First a rapid review of the literature on metrics derived from two generic (EQ-5D and EQ-VAS) and three disease-specific (Oxford Hip Score; Oxford Knee Score; Aberdeen Varicose Vein Questionnaire) PROMs was conducted. Next, the findings of the literature review were mapped onto our typology of metrics to determine their relative frequency of use, Finally, seven group meetings with surgical clinicians (n = 107) and six focus groups with patients (n = 45) were held which were audio-taped, transcribed and analysed thematically.

RESULTS

Only nine studies (9.3% of included papers) used metrics for comparing providers. These were derived from using either the follow-up PROM score (n = 3) or the change in score as an outcome (n = 5), both adjusted for pre-intervention score. There were no recorded uses of the proportion reaching a specified ('good') threshold and only two studies used the proportion reaching a minimally important difference (MID).Surgical clinicians wanted multiple outcomes, with most support expressed for the mean change in score, perceiving it to be more interpretable; there was also some support for the MID. For patients it was apparent that rather than the science behind these measures, the most important aspects were the use of language that would make the metrics personally meaningful and linking the metric to a familiar scale.

CONCLUSIONS

For clinicians the recommended metrics are the mean change in score and the proportion achieving a MID, both adjusted for pre-intervention score. Both need to be clearly described and explained. For patients we recommend the proportion achieving a MID or proportion achieving a significant improvement in hip function, both adjusted for pre-intervention score.

Relationship between patients' reports of complications and symptoms, disability and quality of life after surgery

BACKGROUND

Patient-reported complications are increasingly being used to compare the performance of surgical departments. The objectives of this study were to explore the validity of patient-reported complications and to determine their influence on patients' reports of the benefits of surgery (health gain).

METHODS

This was an observational study of patients in England who underwent hip replacement (68,391), knee replacement (77,705), inguinal hernia repair (48,199) or varicose vein surgery (16,535) during 2009-2011. Health gain was assessed with condition-specific measures of symptoms and disability (Oxford Hip Score, Oxford Knee Score, Aberdeen Varicose Vein Questionnaire), health-related quality of life (EQ-5D™ index) and a single item on the success of surgery. Adverse outcomes included four complications, readmission and further surgery.

RESULTS

There was evidence that patient-reported complications were valid. Patients with three or more co-morbid conditions reported more complications, whereas age, sex and socioeconomic status (adjusted for co-morbidity) had little, or no association. Complications were strongly associated with readmission and further surgery. Among patients reporting a complication, the Oxford Hip Score or Oxford Knee Score was about 3 points (or 15 per cent) lower than the value in patients not reporting a complication. The EQ-5D™ score was about 0·07 lower for joint replacement, 0·06 lower for hernia repair and 0·04 lower for varicose vein surgery.

CONCLUSION

Patients' reports of complications can be used for statistical comparisons of surgical departments. If the relationship between complications and health gain is causal, there is scope for improving health gain indicators after surgery by minimizing the risk of a complication.

Cost and effectiveness of laser with phlebectomies compared with foam sclerotherapy in superficial venous insufficiency. Early results of a randomised controlled trial

OBJECTIVES

Quantify endovenous laser ablation (EVLA) with concurrent phlebectomies and ultrasound-guided foam sclerotherapy (UGFS) in cost and effectiveness at 3 weeks and 3 months.

DESIGN

Single-centre, prospective, randomised controlled trial.

PATIENTS

One hundred patients (100 legs), C(2-6), age 21-78, M:F 42:58, with primary varicose veins received either EVLA under local anaesthetic or UGFS.

METHODS

Assessments included duplex, Aberdeen varicose vein questionnaire (AVVQ), venous clinical severity score (VCSS), venous filling index (VFI), visual analogue 7-day pain score and analgesia requirements. Additional treatments with UGFS were performed, if required. Micro-costing, using individually timed treatments, was based on consumables, staff pay and overheads.

RESULTS

Changes in AVVQ, VCSS and VFI values (3 months) did not demonstrate any significant difference between groups. At 3 months, the above-knee GSV occlusion rate (without co-existing reflux) was not significantly different between the groups (74% vs 69%; EVLA vs UGFS; P = .596). Of the 9 haemodynamic failures in each group, 7 EVLA patients and 4 UGFS patients had co-existing cross-sectional above-knee GSV occlusion at some point. However, UGFS significantly outperformed EVLA in cost, treatment duration, pain, analgesia requirements and recovery.

CONCLUSIONS

UGFS is 3.15 times less expensive than EVLA (£230.24 vs £724.72) with comparable effectiveness but 56% (versus 6%) required additional foam (ISRCTN:03080206).

Sociodemographic differences in the severity and duration of disease amongst patients undergoing hip or knee replacement surgery

BACKGROUND

Differences in the use of hip and knee replacement by sex, age, ethnicity or socioeconomic status may lead to differences in disease severity between those who have surgery.

METHODS

Analyses used data collected from 117,736 patients in 2009-10 via the Patient Reported Outcome Measures (PROMs) programme in England. Adjusted differences were estimated in the Oxford Hip Score (OHS) or the Oxford Knee Score (OKS), both expressed on a scale from 0 to 48, and the proportion with longstanding problems (>5 years), expressed as odds ratios (ORs).

RESULTS

Women had more severe pain and disability than men on average (difference OHS 2.3 and OKS 3.3), but less often longstanding problems. Compared with white patients, average severity was higher in South Asian patients (difference OHS 2.7 and OKS 3.0) and in black patients (difference OHS 0.9 and OKS 1.6), who also more often had longstanding problems (OR 1.40 for hip and 1.54 for knee). Patients from deprived areas had more severe disease (difference OHS 3.6 and OKS 3.3 between least and most deprived quintile).

CONCLUSIONS

There is evidence that non-white and deprived patients tend to have hip and knee replacement surgery at a later stage in the course of their disease.

Outcomes of elective surgery undertaken in independent sector treatment centres and NHS providers in England: audit of patient outcomes in surgery

OBJECTIVE

To compare characteristics of patients and outcomes after elective surgery in independent sector treatment centres (ISTCs) and NHS providers.

DESIGN

Follow-up study with outcomes reported by patients three to six months after surgery.

SETTING

25 ISTCs and 72 NHS providers in England. Population Consecutive patients undergoing hip or knee replacement (5671 in ISTCs and 14,292 in NHS), inguinal hernia repair (640 and 2023, respectively), or surgery for varicose veins (248 and 1336, respectively).

MAIN OUTCOMES

Symptoms and disability reported by patients (Oxford hip and knee scores on a 48 point scale; Aberdeen varicose vein questionnaire) and quality of life (EuroQol EQ-5D score).

RESULTS

Patients in ISTCs were healthier than those in NHS providers, had less severe preoperative symptoms, and were more affluent, though the differences were small. With adjustment, patients undergoing joint replacements in NHS providers had poorer outcomes: difference of -1.7 (95% confidence interval -2.5 to -0.9) on the Oxford hip score and -0.9 (-1.6 to -0.2) on the Oxford knee score. They more often reported complications: odds ratio 1.3 (95% confidence interval 1.1 to 1.5) for hip and 1.4 (1.2 to 1.6) for knee. There were no significant differences in outcomes after surgery for hernia or varicose veins, except that NHS patients more often reported poor results after hernia repair (1.4, 1.0 to 1.9) and additional surgery after varicose vein surgery (2.8, 1.2 to 6.8).

CONCLUSION

Patients undergoing surgery in ISTCs were slightly healthier and had less severe conditions than those undergoing surgery in NHS providers. Some outcomes were better in ISTCs, but differences were small compared with the impact ISTCs could have on the provision of elective services.

Agreement about identifying patients who change over time: cautionary results in cataract and heart failure patients

BACKGROUND

Preference-based measures of health-related quality of life all use the same dead = 0.00 to perfect health = 1.00 scale, but there are substantial differences among measures.

OBJECTIVE

The objective was to examine agreement in classifying patients as better, stable, or worse.

METHODS

The EQ-5D, Health Utilities Index Mark 2 and Mark 3, Quality of Well-Being-Self-Administered scale, Short-Form 36 (Short-Form 6D), and disease-targeted measures were administered prospectively in 2 clinical cohorts. The study was conducted at academic medical centers: University of California, Los Angeles; University of California, San Diego; University of Wisconsin-Madison; and University of Southern California. Patients undergoing cataract extraction surgery with lens replacement completed the 25-item National Eye Institute Visual Function Questionnaire (NEI-VFQ-25). Patients newly referred to congestive heart failure specialty clinics completed the Minnesota Living with Heart Failure Questionnaire (MLHF). In both cohorts, subjects completed surveys at baseline and at 1 and 6 months. The NEI-VFQ-25 and MLHF were used as gold standards to assign patients to categories of change. Agreement was assessed using κ.

RESULTS

There were 376 cataract patients recruited. Complete data for baseline and the 1-month follow-up were available on all measures for 210 cases. Using criteria specified by Altman, agreement was poor for 6 of 9 pairs of comparisons and fair for 3 pairs. There were 160 heart failure patients recruited. Complete data for baseline and the 6-month follow-up were available for 86 cases. Agreement was negligible for 5 pairs and fair for 1. The study was conducted on selected patients at a few academic medical centers.

CONCLUSIONS

The results underscore the lack of interchangeability among different preference-based measures.

Validating the 28-tender joint count using item response theory

OBJECTIVE

To examine the construct validity of the 28-tender joint count (TJC-28) using item response theory (IRT)-based methods.

METHODS

A total of 457 patients with early stage rheumatoid arthritis (RA) were included. Internal construct validity of the TJC-28 was evaluated by determining whether the TJC-28 fit a 2-measure logistic IRT model. As well, we tested whether the discrimination and difficulty parameters of the joints properly reflected the known left-right symmetry of joint involvement. External validity was evaluated by correlations with other established measures of disease activity, including pain, disability, general health, erythrocyte sedimentation rate (ESR), and the 28-swollen joint count.

RESULTS

The TJC-28 showed a good fit with the 2-parameter logistic model, with no relevant differential item functioning across sex, age, and time and with excellent reliability. The 28 joints covered a reasonable range of disease activity, even though they were mainly targeted at patients with moderate or high disease activity levels. The joint parameters reflected the left-right symmetry of joint involvement for all pairs of joints except one. All disease activity measures, except ESR, were significantly correlated with the TJC-28. Most correlations were of the expected magnitude.

CONCLUSION

The TJC-28 showed good internal and acceptable external construct validity for patients with early-stage RA. The IRT analyses did point to some potential limitations of the instrument, a major problem being its limited measurement range. Future research should examine whether instrument modifications might lead to a more robust assessment of disease activity in patients with RA.

Mathematical coupling does not account for the association between baseline severity and minimally important change values

A number of studies have demonstrated a correlation between baseline severity and minimally important change (MIC) values. However, Browne et al. stated that these studies failed to account for "mathematical coupling," and that, therefore, the correlation between baseline severity and MIC values may be spurious. The present article demonstrates that on the level of individual scores, mathematical coupling causes the observed baseline and change scores to correlate even in the absence of any true correlation between these variables. This phenomenon is because of the fact that change scores can only be estimated by subtracting the baseline score from the follow-up score, causing the baseline and change scores to share a common piece of error variance. However, MIC values are always determined on group level, and mathematical coupling does not affect group-level statistics or the correlation of these statistics across groups. Therefore, mathematical coupling does not account for the association between baseline severity and MIC values as suggested by Browne et al.