Sample size calculations in randomised trials: mandatory and mystical
Abstract
Investigators should properly calculate sample sizes before the start of their randomised trials and adequately describe the details in their published report. In these a-priori calculations, determining the effect size to detect--eg, event rates in treatment and control groups--reflects inherently subjective clinical judgments. Furthermore, these judgments greatly affect sample size calculations. We question the branding of trials as unethical on the basis of an imprecise sample size calculation process. So-called underpowered trials might be acceptable if investigators use methodological rigor to eliminate bias, properly report to avoid misinterpretation, and always publish results to avert publication bias. Some shift of emphasis from a fixation on sample size to a focus on methodological quality would yield more trials with less bias. Unbiased trials with imprecise results trump no results at all. Clinicians and patients deserve guidance now.
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Estimates of the rate of the event of interest or other assumptions central to sample size calculations are commonly imprecise, if not guesswork.
“estimates of the rate of the event of interest or other assumptions central to calculations are commonly imprecise, if not guesswork [ 77 ].”
From Strengthening the Reporting of Observational Studies in Epidemiology (STROBE): Explanation and Elaboration (2007) · cites this paper as [77]
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- Authors
- Schulz, K. F., & Grimes, D. A.
- Affiliations
- Family Health International 360 (US)
- Corresponding author
- Schulz, Kenneth F
- Venue
- The Lancet
- Publisher
- Elsevier BV
- Published
- 2005-04
- Volume
- 365
- Issue
- 9467
- Pages
- 1348-1353
- ISSN
- 0099-5355 (ISSN-L)
- 0140-6736
- OpenAlex
- W2095687684
- Cited by
- 549
- References
- 4
- Citations by year
- 2026: 28 · 2025: 30 · 2024: 21 · 2023: 18 · 2022: 17 · 2021: 31 · 2020: 25 · 2019: 30 · 2018: 35 · 2017: 36 · 2016: 29 · 2015: 31 · 2014: 37 · 2013: 35 · 2012: 23
- FWCI
- 21.10
- Type
- journal article
- Language
- en
- Open access
- closed
- Locations
- The Lancet (publishedVersion)
- PubMed (publishedVersion)
- Topics
- Physical Sciences › Mathematics › Statistics and Probability › Statistical Methods in Clinical Trials
- Social Sciences › Decision Sciences › Statistics, Probability and Uncertainty › Meta-analysis and systematic reviews
- Physical Sciences › Mathematics › Statistics and Probability › Statistical Methods in Epidemiology
- Keywords
- sample size determination, randomised trials, effect size estimation, publication bias, trial bias, methodological quality, trial reporting
- MeSH terms
- Statistics as Topic, Randomized Controlled Trials as Topic, Sample Size
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