Different ways to estimate treatment effects in randomised controlled trials

Background

Regarding the analysis of RCT data there is a debate going on whether an adjustment for the baseline value of the outcome variable should be made. When an adjustment is made, there is a lot of misunderstanding regarding the way this should be done. Therefore, the aims of this educational paper are: 1) to explain different methods used to estimate treatment effects in RCTs, 2) to illustrate the different methods with a real life example and 3) to give an advise on how to analyse RCT data.

Methods

Longitudinal analysis of covariance, repeated measures analysis in which also the baseline value is used as outcome and the analysis of changes were theoretically explained and applied to an example dataset investigating a systolic blood pressure lowering treatment.

Results

It was shown that differences at baseline should be taken into account and that regular repeated measures analysis and regular analysis of changes did not adjust for the baseline differences between the groups and therefore lead to biased estimates of the treatment effect. In the real life example, due to the differences at baseline between the treatment and control group, the different methods lead to different estimates of the treatment effect.

Conclusion

Regarding the analysis of RCT data, it is advised to use longitudinal analysis of covariance or a repeated measures analysis without the treatment variable, but with the interaction between treatment and time in the model.

Regressive research: The pitfalls of post hoc data selection in the study of unconscious mental processes

Many studies of unconscious processing involve comparing a performance measure (e.g., some assessment of perception or memory) with an awareness measure (such as a verbal report or a forced-choice response) taken either concurrently or separately. Unconscious processing is inferred when above-chance performance is combined with null awareness. Often, however, aggregate awareness is better than chance, and data analysis therefore employs a form of extreme group analysis focusing post hoc on participants, trials, or items where awareness is absent or at chance. The pitfalls of this analytic approach are described with particular reference to recent research on implicit learning and subliminal perception. Because of regression to the mean, the approach can mislead researchers into erroneous conclusions concerning unconscious influences on behavior. Recommendations are made about future use of post hoc selection in research on unconscious cognition.

Systematic review and meta-analysis: Gastric electrical stimulation for gastroparesis

BACKGROUND

Controlled trials of gastric electrical stimulation (GES) for gastroparesis reported no significant improvement in symptoms, while open label studies suggested substantial clinical benefits.

AIM

To determine if GES is effective in reducing symptoms in patients with gastroparesis.

METHODS

We searched PubMed and Embase for articles published in English (1990-2014) using "gastroparesis" as a search term restricted to "clinical trial". We included studies describing repeated patient-based symptom ratings before and during standardized treatments of at least one week duration.

RESULTS

Five studies randomly allocated patients to periods with or without GES. Total symptom severity (TSS) scores did not differ between these periods (0.17 [95% confidence interval: -0.06 to 0.4]; P=0.15). However, sixteen open label studies of GES showed a significant TSS decrease (2.68 [2.04-3.32]; Q=39.0; P<0.001). Other treatment modalities similarly improved TSS by 1.97 [1.5-2.44] for medical therapy (MED), by 1.52 [0.9-2.15] for placebo arms (PLA), and by 2.32 [1.56-3.06] for botulinum toxin (BTx). There were significant differences in baseline TSS ratings among these studies (GES: 6.28 [6.28-7.42]; MED: 4.76 [4.09-5.42]; PLA: 4.59 [3.77-5.42]; BTx: 6.02 [5.3-6.74]; Q=35.1; P<0.001). Meta-regression analysis showed these baseline differences to significantly impact TSS ratings during treatment (Q=71.8; P<0.001).

CONCLUSION

Independent of the treatment modality, baseline symptom severity impacts treatment results in gastroparesis. Considering the skewed population with refractory symptoms, regression to the mean likely contributes to the substantial discrepancies between the reported results of controlled and open label GES studies, raising questions about the use of GES outside of defined clinical trials.

Good epidemiological practice: a narrative review of appropriate scientific methods to evaluate the impact of antimicrobial stewardship interventions

AIMS

In this narrative review, we provide a framework for assessing the quality of evidence provided by studies investigating antimicrobial stewardship (AMS) interventions, and inform the design and planning stage for future AMS evaluation studies to determine the best strategies to keep antimicrobial resistance at bay.

SOURCES

Cochrane/Pubmed.

CONTENT

As AMS is mostly applied in a complex, real-world setting, bias and random time effects can jeopardize the validity of causal inference. The most important risks include simultaneously implemented infection prevention strategies and regression to the mean. Inclusion of homogeneous intervention and control arms, through randomization of the intervention, can limit these risks. However, contamination can play an important role for AMS; therefore, randomization at cluster-level, instead of randomization at individual-level, is recommended. It can be challenging to identify enough representative clusters, and implementation of a cluster-RCT (cRCT) can be costly. Controlled interrupted time series (ITS) design has a high validity as well, and is relatively straightforward to implement, although time-varying confounding should be considered. Independent of the study design, it is crucial to include multiple process, clinical outcome, microbiological and financial measures, to be able to detect possible, unintended consequences.

IMPLICATIONS

Future studies assessing the impact of new AMS strategies should produce compelling evidence by opting for cRCTs, or ITS including a control arm. Furthermore, a holistic view of intended and unintended consequences should be reported, and a detailed process evaluation should be provided to adequately inform implementation of successful AMS strategies to battle the rising burden of AMR.

Placebo responses in patients with gastrointestinal disorders

Over the last several years there has been a growing interest in placebo, not only as an inert control in clinical trials, but also in the placebo effect as a group effect as well as a reaction in individual subjects. Methodological factors such as regression to the mean and natural history of the disease play a role in the evaluation of a possible placebo effect. In this report, we discuss several factors including Pavlovian conditioning, beliefs outcome, expectations, and other factors as potential mediators of the placebo response. Placebo effects are common in gastrointestinal diseases and there seems to be no clear difference between placebo effects in functional gastrointestinal diseases (functional dyspepsia and irritable bowel syndrome) and organic gastrointestinal disease (duodenal ulcer and inflammatory bowel disease).

Regression to the mean and alcohol consumption: a cohort study exploring implications for the interpretation of change in control groups in brief intervention trials

BACKGROUND

Reductions in drinking among individuals randomised to control groups in brief alcohol intervention trials are common and suggest that asking study participants about their drinking may itself cause them to reduce their consumption. We sought to test the hypothesis that the statistical artefact regression to the mean (RTM) explains part of the reduction in such studies.

METHODS

967 participants in a cohort study of alcohol consumption in New Zealand provided data at baseline and again six months later. We use graphical methods and apply thresholds of 8, 12, 16 and 20 in AUDIT scores to explore RTM.

RESULTS

There was a negative association between baseline AUDIT scores and change in AUDIT scores from baseline to six months, which in the absence of bias and confounding, is RTM. Students with lower baseline scores tended to have higher follow-up scores and conversely, those with higher baseline scores tended to have lower follow-up scores. When a threshold score of 8 was used to select a subgroup, the observed mean change was approximately half of that observed without a threshold. The application of higher thresholds produced greater apparent reductions in alcohol consumption.

CONCLUSIONS

Part of the reduction seen in the control groups of brief alcohol intervention trials is likely to be due to RTM and the amount of change is likely to be greater as the threshold for entry to the trial increases. Quantification of RTM warrants further study and should assist understanding assessment and other research participation effects.

Most evidence for the compensation account of cognitive training is unreliable

Cognitive training and brain stimulation studies have suggested that human cognition, primarily working memory and attention control processes, can be enhanced. Some authors claim that gains (i.e., post-test minus pretest scores) from such interventions are unevenly distributed among people. The magnification account (expressed by the evangelical “who has will more be given”) predicts that the largest gains will be shown by the most cognitively efficient people, who will also be most effective in exploiting interventions. In contrast, the compensation account (“who has will less be given”) predicts that such people already perform at ceiling, so interventions will yield the largest gains in the least cognitively efficient people. Evidence for this latter account comes from reported negative correlations between the pretest and the training/stimulation gain. In this paper, with the use of mathematical derivations and simulation methods, we show that such correlations are pure statistical artifacts caused by the widely known methodological error called “regression to the mean”. Unfortunately, more advanced methods, such as alternative measures, linear models, and control groups do not guarantee correct assessment of the compensation effect either. The only correct method is to use direct modeling of correlations between latent true measures and gain. As to date no training/stimulation study has correctly used this method to provide evidence in favor of the compensation account, we must conclude that most (if not all) of the evidence should be considered inconclusive.

Supplementary guanfacine hydrochloride as a treatment of attention deficit hyperactivity disorder in adults: A double blind, placebo-controlled study

The purpose of this study was to examine the efficacy of an extended release guanfacine hydrochloride supplement relative to a placebo supplement in adults (19-62) with ADHD and a sub-optimal response to a stimulant-only treatment program. The study's primary outcome measures were the Attention Deficit Hyperactivity Disorder Rating Scale and the Clinical Global Impression - Severity. Twenty-six adults who met criteria for attention deficit hyperactivity disorder and sub-optimal functioning were randomly assigned to supplement their existing psychostimulant treatment regimen with either a titrated dose (1-6mg) of extended release guanfacine hydrochloride or a matching placebo for a 10-week trial. The data were analyzed with standard mixed model analysis of variance procedures, and participants in both the investigational agent group and the placebo group showed statistically significant improvement in their symptoms and functioning over the course of the trial. The treatments did not differ in terms of their efficacy, safety, or tolerability. Although these results do suggest that both treatments were associated with clinical improvement, the possible impacts of socially desirable responding and regression to the mean on these results are discussed.

Safety effects of section control--an empirical Bayes evaluation

The safety effects of section control were investigated at 14 sites in Norway. A before-after study was conducted with the empirical Bayes method in order to control for regression to the mean (RTM). Effects of trend, volumes, speed limit changes and speed cameras at some of the sites in the before period are controlled for as well. For injury crashes a non-significant reduction by 12% was found. The number of killed or severely injured was found to be significantly reduced by 49% at the section control sites. The results indicate that the crash reductions in tunnels (most of which are undersea tunnels with section control on steep downhill segments) are at least of the same magnitude as on open roads. The results are consistent with findings from speed measurements, although the crash reductions are larger than one would expect as a result from the speed reductions. Downstream of the section control sites (up to 3 km in each direction) injury crashes were found to be significantly reduced by 46%. The number of KSI downstream of the section control sites is too small for drawing any conclusions. It is concluded that section control is effective in reducing both speed and crashes, especially serious crashes, and that spillover effects (crash reductions at non-enforcement sites) are more likely to occur than crash migration. The size of the effects that were found should be interpreted with caution because of the relatively short after periods for some of the sites and the sensitivity of the results to the outcomes of individual crashes.

Placebo in epilepsy

Placebos impact epilepsy in a number of ways. Through randomized clinical trials, explicit clinical use, and also through implicit clinical use, placebos play a role in epilepsy. This chapter will discuss the reasons placebo is used, the determinants of placebo response in epilepsy, observations about placebo specific to epilepsy, and ways in which clinical trial design is impacted by placebo.

The natural course of shoulder instability and treatment trends: a systematic review

Background

The natural course of shoulder instability is still not entirely clear. We aimed in this review to analyse the current scientific evidence of the natural history of shoulder instability.

Materials and methods

A systematic review of the English literature was performed using the PubMED database throughout January 2014. This review was guided, conducted and reported according to PRISMA criteria. The criteria for inclusion in the study were (1) the article was written in English, (2) the level of evidence was 1–4, (3) the article was available in full text, (4) the article investigated the natural history or course of shoulder instability, the outcome of non-operative management, or the regression of the shoulder symptoms to the mean. The methodological quality of each included study was individually assessed using a newly developed general assessment tool—Assessing the Methodological Quality of Published Papers (AMQPP).

Results

Eight articles related to shoulder instability met the inclusion criteria. Four papers were considered high-quality studies (evidence level 1 and 2). One paper assessed the natural history and the natural course of shoulder instability directly. The other studies indirectly assessed the natural history by studying non-operative and operative therapy trends. We found no articles which clearly referred to the role of ‘regression to the mean’.

Conclusion

Following the natural history and the implementation of standardised non-operative treatment programmes are an effective therapy and superior to surgery in many cases. However, primary acute shoulder dislocation in young active individuals partaking in demanding physical activities could benefit from early surgical intervention. The AMQPP score works as a quick quality-checking tool which helps researchers to identify the key points in each paper and reach a decision regarding the eligibility of the paper more easily. The AMQPP scoring system is still open for further development and expansion.

Level of evidence Level IV.

Safety effects of fixed speed cameras - An empirical Bayes evaluation

The safety effects of 223 fixed speed cameras that were installed between 2000 and 2010 in Norway were investigated in a before-after empirical Bayes study with control for regression to the mean (RTM). Effects of trend, volumes, and speed limit changes are controlled for as well. On road sections between 100m upstream and 1km downstream of the speed cameras a statistically significant reduction of the number of injury crashes by 22% was found. For killed and severely injured (KSI) and on longer road sections none of the results are statistically significant. However, speed cameras that were installed in 2004 or later were found to reduce injury crashes and the number of KSI on road sections from 100m upstream to both 1km and 3km downstream of the speed cameras. Larger effects were found for KSI than for injury crashes and the effects decrease with increasing distance from the speed cameras. At the camera sites (100m up- and down-stream) crash reductions are smaller and non-significant, but highly uncertain and possibly underestimated.

Evaluation of 5536 patients treated in an integrative outpatient tinnitus treatment center-immediate effects and a modeling approach for sustainability

BACKGROUND

Tinnitus is an increasingly serious problem for health care systems. According to epidemiological data, 7-14 % of outpatients have asked their physician about tinnitus and management strategies. Integrative outpatient treatments are currently regarded as promising therapeutic approaches for managing tinnitus. In this article we report on the treatment success of an outpatient tinnitus treatment center in Germany.

METHODS

This cohort study included pre-post data of 5536 outpatients which were treated between 2003 and 2010 in the tinnitus-therapy center, Krefeld-Düsseldorf (TTZ). The intervention consisted of psychological immunization training as well as an auditory stimulation therapy component. The main outcome parameter was the score of the Tinnitus Questionnaire (TQ) which was assessed before and after a 9 days treatment and (in a small subsample) at a 6 months follow-up. Missing data were multiply imputed. Pre-post effect sizes were calculated and adjusted for regression to the mean (RTM).

RESULTS

RTM-adjusted treatment effects at the end of treatment were estimated as -18.6 (CI: -18.9 to 18.2, p < 0.001) score points which corresponds to a standardized effect of d = -1.03 (CI: -1.05 to -1.01). These effects can be corroborated in various subgroups and all subscales of the TQ (d ranging from -0.31 to -0.97).

CONCLUSION

The study suggests the effectiveness of this outpatient tinnitus therapy concept. Multiple imputations techniques and RTM analysis were helpful in carving out true treatment effects.

Interpretation of within-group change in randomised trials

In medicine, it is common to observe improvement after intervention, at least partly because patients present for care in extremis and would have improved without intervention. Controlling for this counterfactual explanation for improvement is the principle reason to conduct a trial in which patients are randomised to treatment or a control group. Accordingly, it is not reasonable to infer that both interventions are effective when the groups show similar improvements in outcome.

Embodiment and learning of abstract concepts (such as algebraic topology and regression to the mean)

This video is a proof of concept that ideas from embodied cognition can be used to understand how the brain and cognitive systems deal with very abstract concepts. The video teaches regression to the mean using three ideas. The first idea is directly related to embodied cognition: abstract concepts are grounded in perceptual, motor, and emotional systems by using successive levels of grounding within an extended procedure. The second idea is that this sort of grounding often requires formal instruction: a teacher needs to develop the sequence in which the concepts are grounded and the methods of grounding. That is, at least some abstract concepts are unlikely to be learned through an individual's unstructured interactions with the world. The third idea is that humans are hyper-social, thus making formal instruction possible. To the extent that the viewer learns the abstract concept of regression to the mean, then the video demonstrates how an embodied theory of abstract concepts could work.

Comparison of Bayesian techniques for the before-after evaluation of the safety effectiveness of short 2+1 road sections

In evaluating the effectiveness of a road safety treatment, the regression to the mean phenomenon is a cause for concern because of a possible overestimation of benefits. Therefore, Bayesian approaches are usually suggested as the most appropriate methodologies for before-after studies as they account for regression to the mean effects. The empirical Bayes (EB) methodology examines the estimation of the expected number of crashes that would have occurred without treatment and compares them with the crashes observed at the treated sites. Even if there is no significant regression to the mean bias, the EB technique requires a reliable and large dataset with sufficient years of observation and number of treated sites, adequate for estimating the safety effects of a treatment with acceptable standard errors. In this framework, a full Bayesian (FB) approach can mitigate the problem of using small datasets by providing more detailed causal inferences and more flexibility in selecting crash count distributions, acknowledging that a more complex methodology must be applied. With the aim of estimating the safety improvements of new, short 2 + 1 road sections in Poland limited by the existing road network, EB and FB estimations are compared and different safety performance function (SPF) model forms are used in order to evaluate the performance of the two methodologies. Results indicated that, even if crash modification factors (CMFs) resulted in similar average values, the EB trend is to underestimate CMFs compared with the more complex methodology, while overall the FB approach provided a lower standard deviation. The differences are more pronounced between the EB and FB approaches when a simple SPF model form is used for the analysed dataset. Moreover, for this specific dataset, the difference between the FB method and the EB method using a refined regression model with more variables was negligible.

Regression to the Mean in Measurements of Growth Rates in Geographic Atrophy

INTRODUCTION

Comparison of patients with extremely high and low values of a given characteristic is a common strategy to gain insights into disease mechanisms, but this approach is particularly susceptible to regression to the mean (RTM).

OBJECTIVE

The aim of this work was to determine RTM in growth rate measurements in patients with geographic atrophy (GA) secondary to age-related macular degeneration.

METHODS

We conducted a retrospective analysis of the GAIN (NCT01694095) and its extension study, in which individuals 50 years or older with pure GA were followed for a minimum of 6 months. Two repeated and masked measurements of area of atrophy, both at baseline and final visits, were made, and growth rates were calculated for each. RTM was determined graphically and statistically, and the percentage of eyes misclassified as having fast and slow progression rates due to RTM was determined for different definitions of "fast" and "slow" growth.

RESULTS

We included 112 eyes of 112 patients: 64.3% were females, the mean age was 78.1 (SD ±7.6) years, and the mean follow-up time was 3.2 (±2.2) years. There was RTM, which decreased when the mean of two measurements was used. The magnitude of RTM in growth rates ranged from 2 to 11 µm/year and led to misclassification of eyes considered to have fast and slow growth between 2.9 and 10.3% of the cases, depending on the definition of fast and slow growth.

CONCLUSIONS

RTM was present in measurements of GA growth rate, but it had a modest impact on patient misclassification. Comparison of features between patients with extreme growth rates is a reasonable strategy, but RTM should be minimized by taking the mean of two measurements.

Regression to the mean in latent change score models: an example involving breastfeeding and intelligence

BACKGROUND

Latent change score models are often used to study change over time in observational data. However, latent change score models may be susceptible to regression to the mean. Earlier observational studies have identified a positive association between breastfeeding and child intelligence, even when adjusting for maternal intelligence.

METHOD

In the present study, we investigate regression to the mean in the case of breastfeeding and intelligence of children. We used latent change score modeling to analyze intergenerational change in intelligence, both from mothers to children and backward from children to mothers, in the 1979 National Longitudinal Survey of Youth (NLSY79) dataset (N = 6283).

RESULTS

When analyzing change from mothers to children, breastfeeding was found to have a positive association with intergenerational change in intelligence, whereas when analyzing backward change from children to mothers, a negative association was found.

CONCLUSIONS

These discrepant findings highlight a hidden flexibility in the analytical space and call into question the reliability of earlier studies of breastfeeding and intelligence using observational data.

Francis Galton's regression towards mediocrity and the stability of types

A prevalent narrative locates the discovery of the statistical phenomenon of regression to the mean in the work of Francis Galton. It is claimed that after 1885, Galton came to explain the fact that offspring deviated less from the mean value of the population than their parents did as a population-level statistical phenomenon and not as the result of the processes of inheritance. Arguing against this claim, we show that Galton did not explain regression towards mediocrity statistically, and did not give up on his ideas regarding an inheritance process that caused offspring to revert to the mean. While the common narrative focuses almost exclusively on Galton's statistics, our arguments emphasize the anthropological and biological questions that Galton addressed. Galton used regression towards mediocrity to support the claim that some biological types were more stable than others and hence were resistant to evolutionary change. This view had implications concerning both natural selection and eugenics. The statistical explanation attributed to Galton appeared later, during the biometrician-mutationist debate in the early 1900s. It was in the context of this debate and specifically by the biometricians, that the development of the statistical explanation was originally attributed to Galton.

Identifying predictors of resilience to stressors in single-arm studies of pre-post change

Many older adults experience a major stressor at some point in their lives. The ability to recover well after a major stressor is known as resilience. An important goal of geriatric research is to identify factors that influence resilience to stressors. Studies of resilience in older adults are typically conducted with a single-arm where everyone experiences the stressor. The simplistic approach of regressing change versus baseline yields biased estimates due to mathematical coupling and regression to the mean (RTM). We develop a method to correct the bias. We extend the method to include covariates. Our approach considers a counterfactual control group and involves sensitivity analyses to evaluate different settings of control group parameters. Only minimal distributional assumptions are required. Simulation studies demonstrate the validity of the method. We illustrate the method using a large, registry of older adults (N  =7239) who underwent total knee replacement (TKR). We demonstrate how external data can be utilized to constrain the sensitivity analysis. Naive analyses implicated several treatment effect modifiers including baseline function, age, body-mass index (BMI), gender, number of comorbidities, income, and race. Corrected analysis revealed that baseline (pre-stressor) function was not strongly linked to recovery after TKR and among the covariates, only age and number of comorbidities were consistently and negatively associated with post-stressor recovery in all functional domains. Correction of mathematical coupling and RTM is necessary for drawing valid inferences regarding the effect of covariates and baseline status on pre-post change. Our method provides a simple estimator to this end.

Design and analysis considerations for first treatment escalation in clinical trials

Protocol-mandated, outcome-driven treatment adaptations are common in many types of clinical trials, and a prominent feature of so-called treat-to-target trials. Successive treatment escalation (dosage increase or addition of a drug) if disease activity targets are not reached is a typical design element in these studies. Focusing on the first treatment escalation step, here we address ways of estimating the effect of this outcome-based intervention as well some issues pertaining to the design of such treatment changes in randomized trials. Estimating escalation effects requires to disentangle them from concurrent effects, including persisting effects of the randomized treatment and regression to the mean. A regression-based method and a likelihood ratio test were adapted and assessed in simulations and in data from a recent treat-to-target study in rheumatoid arthritis. In simulations, the procedures were satisfactory in terms of bias and sensitivity with some advantage for the likelihood ratio test. They were able to identify evidence for the escalation effect in the examined study. In summary, both analysis methods are useful, but are sensitive to key assumptions and rely on compliance to the protocol as well as frequent and complete assessments. Furthermore, we examined different treatment escalation designs, including escalation at multiple time points (early escalation). If a longitudinal model for the disease activity is available, we describe how early escalation strategies can decrease the overall disease burden. We provide recommendations for the design of treatment escalation procedures in typical settings.

Baseline adjustment increases accurate interpretation of posturographic sway scores

Postural steadiness may be quantified using posturographic sway measures. These measures are commonly used to differentiate between a person's baseline balance and balance related to some physiological condition. However, the difference in sway scores between the two conditions may be difficult to detect due to large inter-subject variation. We compared detection accuracy provided by three models that linearly regress a sway measure (mean distance, velocity, or frequency) on the effect of eye closure on balance (eyes open (EO) vs. eyes closed (EC)). In Model 1 the dependent variable is a single sway score (EO or EC), whereas in Models 2 and 3 it is a change score (EO-EO or EC-EO). The independent variable is always the group (group=0: EO or group=1: EC). Model 3 also accounts for the regression to the mean effect (RTM), by considering the baseline value (EO) as a covariate. When differentiating between EO and EC conditions, 94% accuracy can be achieved when using mean velocity as sway measure and either Model 2 or 3. Thus by adjusting for baseline score one increases the accurate interpretation of posturographic sway scores.

Treatment effects in pharmacological clinical randomized controlled trials are mainly due to placebo

OBJECTIVES

The placebo response in clinical trials has four components: regression to the mean (RTM), measurement artifacts, natural tendency (NT) of the disease, and the genuine placebo effect. Our objective is to determine what contributes to the size of the placebo-effect in clinical trials by meta-regressions of randomized placebo-controlled clinical trials.

STUDY DESIGN AND SETTING

We identified five diseases where data on the rates of NT were available to search for a sample of n = 150 (5x30) randomized controlled trials. We extracted various study descriptors and performed meta-regressions to predict improvement in treatment and placebo groups.

RESULTS

We sampled 30 trials each from the following diagnoses: osteoarthritis of the knee, irritable bowel syndrome, depression, sleep disorders, migraine, and extracted relevant information. We estimated the effects due to RTM and NT and analyzed the improvement in placebo and treatment groups by fitting two regression models. Both models were highly significant, explaining 72% of the variance. Improvement in the placebo group can be significantly predicted by improvement in the treatment group (beta = .84), whether a study was analyzed according to intention to treat (beta = -.10) or was a multicenter study (beta = .12). Improvement in the treatment group can be explained by the improvement in the placebo group (beta = .83), whether a study was a multicenter trial (beta = -.16), and by RTM (beta = -.18). The treatment effect is smaller in sleep studies (beta = -.17).

CONCLUSION

The high correlation of r = .73 between placebo improvement and treatment improvement rates is genuine and not explainable by study or disease characteristics. We conclude from our data that the placebo-effect is the major driver of treatment effects in clinical trials that alone explains 69% of the variance. This leaves only limited space for effects due to pharmacological substances. Context effects are more important than pharmacological ones in the conditions studied by us.

Counting your chickens before they hatch: improvements in an untreated chronic pain population, beyond regression to the mean and the placebo effect

Introduction

Isolating the effect of an intervention from the natural course and fluctuations of a condition is a challenge in any clinical trial, particularly in the field of pain. Regression to the mean (RTM) may explain some of these observed fluctuations.

Objectives

In this paper, we describe and quantify the natural trajectory of questionnaire scores over time, based on initial scores.

Methods

Twenty-seven untreated chronic low back pain patients and 25 healthy controls took part in this observational study, wherein they were asked to complete an array of questionnaires commonly used in pain studies during each of 3 visits (V1, V2, V3) at the 2-month interval. Scores at V1 were classified into 3 subgroups (extremely high, normal, and extremely low), based on z-scores. The average delta (∆ = V2 - V1) was calculated for each subgroup, for each questionnaire, to describe the evolution of scores over time based on initial scores. This analysis was repeated with the data for V2 and V3.

Results

Our results show that high initial scores were widely followed by more average scores, while low initial scores tended to be followed by similar (low) scores.

Conclusion

These trajectories cannot be attributable to RTM alone because of their asymmetry, nor to the placebo effect as they occurred in the absence of any intervention. However, they could be the result of an Effect of Care, wherein participants had meaningful improvements simply from taking part in a study. The improvement observed in patients with high initial scores should be carefully taken into account when interpreting results from clinical trials.

Perceptual narrowing continues throughout childhood: Evidence from specialization of face processing

Face recognition shows a long trajectory of development and is known to be closely associated with the development of social skills. However, it is still debated whether this long trajectory is perceptually based and what the role is of experience-based refinements of face representations throughout development. We examined the effects of short and long-term experienced stimulus history on face processing, using regression biases of face representations towards the experienced mean. Children and adults performed same-different judgments in a serial discrimination task where two consecutive faces were drawn from a distribution of morphed faces. The results show that face recognition continues to improve after 9 years of age, with more pronounced improvements for own-race faces. This increased narrowing with age is also indicated by similar use of stimulus statistics for own-race and other-race faces in children, contrary to the different use of the overall stimulus history for these two face types in adults. Increased face proficiency in adulthood renders the perceptual system less tuned to other-race face statistics. Altogether, the results demonstrate associations between levels of specialization and the extent to which perceptual representations become narrowly tuned with age.