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Related Experiment Video

Updated: Apr 16, 2026

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Failure to look beyond blocks is a mistake.

V W Berger1

  • 1Vance W. Berger, PhD, National Cancer Institute and University of Maryland Baltimore County, Biometry Research Group, National Cancer Institute, 9609 Medical Center Drive, Rockville, MD 20850, USA,

Methods of Information in Medicine
|March 13, 2015
PubMed
Summary
This summary is machine-generated.

Permuted block randomization in clinical trials can lead to chronological bias, a problem researchers often overlook. Addressing this requires balancing chronological and selection bias, which may necessitate methods beyond simple permuted blocks.

Keywords:
Chronological biasmaximal procedurepermuted blocksselection bias

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Area of Science:

  • Clinical Trial Design
  • Biostatistics
  • Research Methodology

Background:

  • Chronological bias is a significant concern in trial design, often stemming from the use of permuted blocks without full understanding.
  • Researchers must recognize the underlying reasons for employing specific randomization techniques like permuted blocks.

Discussion:

  • Permuted block randomization presents a conflict between mitigating chronological bias (favoring small block sizes) and selection bias (favoring large block sizes).
  • The inherent tension between these two biases complicates the straightforward application of permuted blocks in clinical trials.

Key Insights:

  • Understanding chronological bias is crucial for informed discussions on the merits of permuted block randomization.
  • Selection bias presents a counteracting challenge, as solutions for chronological bias can exacerbate selection bias.

Outlook:

  • Exploring randomization methods beyond permuted blocks is essential to overcome the limitations imposed by the chronological and selection bias conflict.
  • Future trial designs may benefit from advanced randomization strategies that effectively manage both chronological and selection biases.