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Related Experiment Videos

Statistical power, sample size, and their reporting in randomized controlled trials

D Moher1, C S Dulberg, G A Wells

  • 1Clinical Epidemiology Unit, Loeb Medical Research Institute, Ottawa Civic Hospital, Ontario, Canada.

JAMA
|July 13, 1994
PubMed
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Most randomized controlled trials (RCTs) with negative results lack sufficient statistical power and adequate sample size calculations. Reporting of sample size calculations has improved, but power to detect meaningful differences remains low over time.

Area of Science:

  • Medical Research Methodology
  • Clinical Trial Design
  • Statistical Analysis in Medicine

Background:

  • Randomized controlled trials (RCTs) are crucial for evidence-based medicine.
  • Negative results in RCTs require careful interpretation regarding statistical power and sample size.
  • Assessing trends in reporting statistical power and sample size calculations is essential for improving research quality.

Purpose of the Study:

  • To analyze the trends in statistical power and sample size calculation reporting in published RCTs with negative results.
  • To evaluate the adequacy of sample sizes in negative RCTs over time.
  • To assess the reporting of clinical significance in negative RCTs.

Main Methods:

  • A descriptive survey of RCTs published in major medical journals (JAMA, Lancet, NEJM) in 1975, 1980, 1985, and 1990.

Related Experiment Videos

  • Calculation of statistical power for negative result trials with simple two-group parallel designs.
  • Development of criteria to classify trial results and identify primary outcomes.

    • Main Results:

    • 27% of reviewed RCTs yielded negative results, a proportion that remained stable.
    • Only 16% and 36% of negative result trials had sufficient power (80%) to detect 25% and 50% relative differences, respectively.
    • Reporting of sample size calculations improved from 0% in 1975 to 43% in 1990, but only 20% of negative trials discussed clinical significance.

    Conclusions:

    • Most negative RCTs are underpowered to detect clinically relevant differences, a situation unchanged over time.
    • Improvements in reporting sample size calculations are noted, but statistical power remains inadequate.
    • There is a need to enhance the reporting of statistical power, sample size calculations, and clinical significance in negative RCTs.