Interpreting the Results of a Retrospective Comparison of Test and Reference Treatments in a Randomized Clinical Trial Setting

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Abstract

Background and Objectives

The retrospective comparison of test and reference treatment arms in a randomized prospective clinical trial is potentially useful in economic modeling seeking to assess the cost effectiveness of alternative therapies.

Methods

To enhance the credibility of such retrospective comparisons, we propose the application of the following adjustments to significance levels obtained from standard statistical methodology: (1) a significance test for the lower bound of the 95 % confidence interval for the observed difference, (2) a conservative Bonferroni method of adjustment for multiple comparisons, (3) an adjusted p-value calculated using Scheffe’s single-step method, and (4) Bayesian 95 % credibility intervals with a prior centered at zero.

Results

These adjustments were applied to data from a randomized double-blind concurrent trial (SPD489-325) that established the efficacy and safety of lisdexamfetamine dimesylate (LDX) in children and adolescents with attention-deficit/hyperactivity disorder (ADHD). Prospectively planned analyses demonstrated that the reduction in the symptoms of ADHD was significantly greater than placebo in patients treated with either LDX or the reference treatment, osmotic-release oral system methylphenidate (OROS-MPH). Retrospective analyses showed that the improvement in the symptoms of ADHD was greater in patients treated with LDX than OROS-MPH. We now show that this observation remained significant after the application of the four statistical penalties.

Conclusions

By adjusting the significance level, it is possible to compare quantitatively such retrospective results with prospectively defined comparisons. However, the qualitative level of such retrospective evidence should remain secondary to that obtained from prospectively specified comparisons in a randomized clinical trial.

Related collections

Most cited references 12

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Treating individuals 2. Subgroup analysis in randomised controlled trials: importance, indications, and interpretation.

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Large pragmatic trials provide the most reliable data about the effects of treatments, but should be designed, analysed, and reported to enable the most effective use of treatments in routine practice. Subgroup analyses are important if there are potentially large differences between groups in the risk of a poor outcome with or without treatment, if there is potential heterogeneity of treatment effect in relation to pathophysiology, if there are practical questions about when to treat, or if there are doubts about benefit in specific groups, such as elderly people, which are leading to potentially inappropriate undertreatment. Analyses must be predefined, carefully justified, and limited to a few clinically important questions, and post-hoc observations should be treated with scepticism irrespective of their statistical significance. If important subgroup effects are anticipated, trials should either be powered to detect them reliably or pooled analyses of several trials should be undertaken. Formal rules for the planning, analysis, and reporting of subgroup analyses are proposed.

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Adjusted P-Values for Simultaneous Inference

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European, randomized, phase 3 study of lisdexamfetamine dimesylate in children and adolescents with attention-deficit/hyperactivity disorder.

David Coghill, Tobias Banaschewski, Michel Lecendreux … (2013)

This study evaluated the efficacy and safety of lisdexamfetamine dimesylate (LDX) compared with placebo in children and adolescents with attention-deficit/hyperactivity disorder (ADHD) in Europe. Osmotic-release oral system methylphenidate (OROS-MPH) was included as a reference arm. Patients (6-17 years old) with a baseline ADHD Rating Scale version IV (ADHD-RS-IV) total score ≥ 28 were randomized (1:1:1) to dose-optimized LDX (30, 50, or 70 mg/day), OROS-MPH (18, 36, or 54 mg/day) or placebo for 7 weeks. Primary and key secondary efficacy measures were the investigator-rated ADHD-RS-IV and the Clinical Global Impressions-Improvement (CGI-I) rating, respectively. Safety assessments included treatment-emergent adverse events (TEAEs), electrocardiograms, and vital signs. Of 336 patients randomized, 196 completed the study. The difference between LDX and placebo in least squares mean change in ADHD-RS-IV total score from baseline to endpoint was -18.6 (95% confidence interval [CI]: -21.5 to -15.7) (p<0.001; effect size, 1.80). The difference between OROS-MPH and placebo in least squares mean change in ADHD-RS-IV total score from baseline to endpoint was -13.0 (95% CI: -15.9 to -10.2) (p<0.001; effect size, 1.26). The proportions (95% CI) of patients showing improvement (CGI-I of 1 or 2) at endpoint were 78% (70-86), 14% (8-21), and 61% (51-70) for LDX, placebo, and OROS-MPH. The most common TEAEs for LDX were decreased appetite, headache, and insomnia. Mean changes in vital signs were modest and consistent with the known profile of LDX. LDX was effective and generally well tolerated in children and adolescents with ADHD.

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Author and article information

Contributors

Moshe Fridman: fmoshe@amf-consulting.com

Journal

Journal ID (nlm-ta): Clin Drug Investig

Journal ID (iso-abbrev): Clin Drug Investig

Title: Clinical Drug Investigation

Publisher: Springer International Publishing (Cham )

ISSN (Print): 1173-2563

ISSN (Electronic): 1179-1918

Publication date (Electronic): 20 December 2014

Publication date PMC-release: 20 December 2014

Publication date (Print): 2015

Volume: 35

Pages: 133-140

Affiliations

[ ]AMF Consulting, Inc., Los Angeles, CA USA

[ ]Shire Development LLC, Wayne, PA USA

Article

Publisher ID: 263

DOI: 10.1007/s40261-014-0263-5

PMC ID: 4300432

PubMed ID: 25526678

SO-VID: 033a9de5-9405-4e57-8971-9d5b5a18d651

License:

Open AccessThis article is distributed under the terms of the Creative Commons Attribution Noncommercial License which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and the source are credited.