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Adaptive increase in sample size when interim results are promising: a practical guide with examples.

Cyrus R Mehta1, Stuart J Pocock

  • 1Cytel Corporation, 675 Massachusetts Avenue, Cambridge, MA 02139, USA. mehta@cytel.com

Statistics in Medicine
|November 23, 2011
PubMed
Summary

Adaptive sample size re-estimation in phase 3 clinical trials offers benefits by staging resource investment. This approach, when interim results are promising, allows conventional inference while preserving type-1 error, making adaptive trials more practical.

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Area of Science:

  • Clinical Trials Methodology
  • Biostatistics
  • Pharmaceutical Research

Background:

  • Traditional fixed sample and group sequential designs are standard in phase 3 trials.
  • Adaptive sample size re-estimation offers potential advantages but faces challenges.
  • Controversy exists regarding non-standard statistical methods for type-1 error preservation in adaptive designs.

Purpose of the Study:

  • To evaluate the benefits and limitations of adaptive sample size re-estimation in phase 3 clinical trials.
  • To compare adaptive designs with fixed and group sequential designs.
  • To define conditions for using conventional inference with adaptive sample size increases while preserving type-1 error.

Main Methods:

  • Comparative analysis of adaptive, fixed, and group sequential trial designs.
  • Case studies from neurology and cardiology trials illustrating adaptive design benefits.
  • Methodological examination of statistical inference under adaptive sample size adjustments.

Main Results:

  • Adaptive designs allow staged investment of resources, committing more sample size only if interim results are promising.
  • In specific settings, adaptive strategies can be more advantageous than fixed or group sequential approaches.
  • Dispensing with non-standard inference is possible when sample size increases are contingent on promising interim data.

Conclusions:

  • Adaptive sample size re-estimation can be more advantageous than traditional designs in certain clinical trial settings.
  • Defining conditions for conventional inference preserves type-1 error and enhances the implementability of adaptive designs.
  • Addressing methodological, regulatory, and operational issues is key to wider adoption of adaptive trial size increases.