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Stratified randomization for clinical trials

W N Kernan1, C M Viscoli, R W Makuch

  • 1Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut, USA.

Journal of Clinical Epidemiology
|February 11, 1999
PubMed
Summary
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Stratified randomization ensures balanced treatment groups, preventing bias in clinical trials. It is most beneficial for small trials where prognostic factors significantly impact outcomes.

Area of Science:

  • Clinical Trials Methodology
  • Biostatistics
  • Medical Research Design

Background:

  • The utility of stratified randomization in clinical trials is debated, causing uncertainty among researchers and readers.
  • Stratification aims to prevent imbalances in treatment groups concerning prognostic factors.

Purpose of the Study:

  • To review the purpose, indications, accomplishments, and alternatives of stratified randomization.
  • To clarify the importance and application of stratification in clinical trial design.

Main Methods:

  • Conducted a Medline search from 1966-1997 to identify relevant research papers.
  • Included 33 articles focusing on stratification and relevant textbooks.

Main Results:

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  • Stratified randomization prevents imbalance for known prognostic factors, potentially reducing type I error and increasing power in small trials (<400 patients) with strong prognostic factors.
  • Stratification impacts sample size in active control equivalence trials but not superiority trials.
  • Theoretical benefits include facilitating subgroup and interim analyses.

    • Conclusions:

    • Stratified randomization is crucial for small trials influenced by prognostic factors, large trials with planned interim analyses, and equivalence trials.
    • Careful selection of stratification factors and their inclusion in analysis are essential upon deciding to stratify.