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Trials which randomize practices II: sample size

S M Kerry1, J M Bland

  • 1Division of General Practice and Primary Care, St George's Hospital Medical School, London, UK.

Family Practice
|April 4, 1998
PubMed
Summary
This summary is machine-generated.

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Sample size calculations for practice-randomized trials must estimate the number of practices, not just patients. Randomizing practices reduces study power, especially with many patients per practice, potentially compromising group comparability.

Area of Science:

  • Clinical Trials Methodology
  • Health Services Research
  • Biostatistics

Background:

  • Sample size calculations are crucial for intervention effectiveness trials.
  • When practices are randomized, calculations must focus on the number of practices, not solely patients.

Purpose of the Study:

  • Introduce methodology for accurate sample size calculation in practice-randomized trials.
  • Discuss the impact of study design on statistical power.

Main Methods:

  • Utilized a worked example from general practice to illustrate the methodology.
  • Applied principles of statistical power analysis to different randomization designs.

Main Results:

  • Practice-randomized designs exhibit lower statistical power compared to patient-randomized designs.

Related Experiment Videos

  • Power loss is significant when few practices are randomized, particularly with large patient cohorts per practice.

    • Conclusions:

    • Avoid studies randomizing few practices due to substantial power loss.
    • Simple randomization of practices may not guarantee intervention group comparability.
    • Accurate sample size estimation is vital for robust trial outcomes.