Subgroup analyses in randomized controlled trials frequently categorized continuous subgroup information.
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Embargo End Date
ICR Authors
Authors
Williamson, SF
Grayling, MJ
Mander, AP
Noor, NM
Savage, JS
Yap, C
Wason, JMS
Grayling, MJ
Mander, AP
Noor, NM
Savage, JS
Yap, C
Wason, JMS
Document Type
Journal Article
Date
2022-07-02
Date Accepted
2022-06-28
Abstract
BACKGROUND AND OBJECTIVES: To investigate how subgroup analyses of published Randomized Controlled Trials (RCTs) are performed when subgroups are created from continuous variables. METHODS: We carried out a review of RCTs published in 2016-2021 that included subgroup analyses. Information was extracted on whether any of the subgroups were based on continuous variables and, if so, how they were analyzed. RESULTS: Out of 428 reviewed papers, 258 (60.4%) reported RCTs with a subgroup analysis. Of these, 178/258 (69%) had at least one subgroup formed from a continuous variable and 14/258 (5.4%) were unclear. The vast majority (169/178, 94.9%) dichotomized the continuous variable and treated the subgroup as categorical. The most common way of dichotomizing was using a pre-specified cutpoint (129/169, 76.3%), followed by a data-driven cutpoint (26/169, 15.4%), such as the median. CONCLUSION: It is common for subgroup analyses to use continuous variables to define subgroups. The vast majority dichotomize the continuous variable and, consequently, may lose substantial amounts of statistical information (equivalent to reducing the sample size by at least a third). More advanced methods that can improve efficiency, through optimally choosing cutpoints or directly using the continuous information, are rarely used.
Citation
Journal of Clinical Epidemiology, 2022, 150 pp. 72 - 79
Source Title
Journal of Clinical Epidemiology
Publisher
ELSEVIER SCIENCE INC
ISSN
0895-4356
eISSN
1878-5921
1878-5921
1878-5921
Collections
Research Team
Clin Trials & Stats Unit