Reporting of sample size calculation in randomised controlled trials: review
Open accessAbstract
OBJECTIVES: To assess quality of reporting of sample size calculation, ascertain accuracy of calculations, and determine the relevance of assumptions made when calculating sample size in randomised controlled trials. DESIGN: Review. DATA SOURCES: We searched MEDLINE for all primary reports of two arm parallel group randomised controlled trials of superiority with a single primary outcome published in six high impact factor general medical journals between 1 January 2005 and 31 December 2006. All extra material related to design of trials (other articles, online material, online trial registration) was systematically assessed. Data extracted by use of a standardised form included parameters required for sample size calculation and corresponding data reported in results sections of articles. We checked completeness of reporting of the sample size calculation, systematically replicated the sample size calculation to assess its accuracy, then quantified discrepancies between a priori hypothesised parameters necessary for calculation and a posteriori estimates. RESULTS: Of the 215 selected articles, 10 (5%) did not report any sample size calculation and 92 (43%) did not report all the required parameters. The difference between the sample size reported in the article and the replicated sample size calculation was greater than 10% in 47 (30%) of the 157 reports that gave enough data to recalculate the sample size. The difference between the assumptions for the control group and the observed data was greater than 30% in 31% (n=45) of articles and greater than 50% in 17% (n=24). Only 73 trials (34%) reported all data required to calculate the sample size, had an accurate calculation, and used accurate assumptions for the control group. CONCLUSIONS: Sample size calculation is still inadequately reported, often erroneous, and based on assumptions that are frequently inaccurate. Such a situation raises questions about how sample size is calculated in randomised controlled trials.
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A complete description of the sample size calculation in the protocol enables an assessment of whether the trial will be adequately powered to detect a minimal clinically important difference.
“A complete description of the sample size calculation in the protocol enables an assessment of whether the trial will be adequately powered to detect a minimal clinically important difference.293”
From SPIRIT 2025 explanation and elaboration: updated guideline for protocols of randomised trials (2025) · cites this paper as [293]
Sample-size calculation is poorly reported in articles of trials and can be inaccurate.
“and sample-size calculation is poorly reported in articles of trials and can be inaccurate [15].”
From Reporting of analyses from randomized controlled trials with multiple arms: a systematic review (2013) · cites this paper as [15]
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- Authors
- Charles, P., Giraudeau, B., Dechartres, A., Baron, G., & Ravaud, P.
- Affiliations
- Inserm (FR)
- Université de Tours (FR)
- Corresponding author
- Ravaud, P.
- Venue
- BMJ
- Publisher
- BMJ
- Published
- 2009-05-12
- Volume
- 338
- Issue
- may12 1
- Pages
- b1732-b1732
- ISSN
- 0007-1447 (ISSN-L)
- 0959-8138
- 1468-5833
- PMC
- PMC2680945
- OpenAlex
- W2039964888
- Cited by
- 274
- References
- 33
- Citations by year
- 2026: 13 · 2025: 17 · 2024: 19 · 2023: 16 · 2022: 13 · 2021: 19 · 2020: 16 · 2019: 21 · 2018: 23 · 2017: 15 · 2016: 14 · 2015: 15 · 2014: 24 · 2013: 14 · 2012: 14
- FWCI
- 9.68
- Type
- journal article
- Language
- en
- Open access
- hybrid
- doi.org
- Licence
- cc-by-nc
- Locations
- BMJ (publishedVersion, cc-by-nc)
- PubMed Central (publishedVersion, cc-by-nc)
- 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, reporting quality, randomized controlled trials, statistical power, a priori assumptions, trial design, primary outcomes, methodological quality
- MeSH terms
- Data Collection, Sensitivity and Specificity, Randomized Controlled Trials as Topic, Sample Size
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