The DOI matches its Crossref record; 16 of the 16 references it cites were found in a registry or an index.
Underpowering in randomized trials reporting a sample size calculation
Abstract
Objective The objective of this study was to determine whether standard deviations (SDs) used in sample size calculations are smaller than those found in the resulting study sample, thereby leading to underpowered studies.Method The predicted SD used in the sample size calculation and the actual SD of the study sample were recorded for randomized trials recently published in one of four major journals.Results Sample SD was greater than predicted SD for 80% of endpoints. About one quarter of trials required five times as many patients as specified in the sample size calculation.Conclusion Trials reporting sample size calculations for continuous endpoints published in the most reputable medical journals are often underpowered. There seems to be insufficient understanding that the SD of a sample of patients is a random variable, associated with imprecision, that cannot easily be extrapolated from one population to another.
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“The values of certain prespecified variables tend to be inappropriately inflated (eg, clinically important target difference) or underestimated (eg, standard deviation for continuous outcomes),295 leading to trials ultimately having less power than originally intended.”
From SPIRIT 2025 explanation and elaboration: updated guideline for protocols of randomised trials (2025) · cites this paper as [295]
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SPIRIT 2013 explanation and elaboration: guidance for protocols of clinical trials
Chan, A.-W., Tetzlaff, J. M., Gotzsche, P. C., Altman, D. G., Mann, H., Berlin, J. A., Dickersin, K., Hrobjartsson, A., Schulz, K. F., Parulekar, W. R., et al. (2013) · BMJ · doi:10.1136/bmj.e7586 · Cited by 6,251
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Metadata
- Authors
- Vickers, A. J.
- Affiliations
- Memorial Sloan Kettering Cancer Center (US)
- Corresponding author
- Vickers, Andrew J
- ORCID
- Vickers, Andrew J
- Venue
- Journal of Clinical Epidemiology
- Publisher
- Elsevier BV
- Published
- 2003-08
- Volume
- 56
- Issue
- 8
- Pages
- 717-720
- ISSN
- 0895-4356 (ISSN-L)
- OpenAlex
- W1999562241
- Cited by
- 102
- References
- 16
- Citations by year
- 2026: 3 · 2025: 5 · 2024: 6 · 2023: 1 · 2022: 3 · 2021: 4 · 2020: 4 · 2019: 1 · 2018: 6 · 2017: 4 · 2016: 7 · 2015: 6 · 2014: 7 · 2013: 10 · 2012: 3
- FWCI
- 5.16
- Type
- journal article
- Language
- en
- Open access
- closed
- Locations
- Journal of Clinical Epidemiology (publishedVersion)
- PubMed (publishedVersion)
- Topics
- Physical Sciences › Mathematics › Statistics and Probability › Statistical Methods in Clinical Trials
- Physical Sciences › Mathematics › Statistics and Probability › Statistical Methods in Epidemiology
- Social Sciences › Decision Sciences › Statistics, Probability and Uncertainty › Meta-analysis and systematic reviews
- Keywords
- underpowered trials, sample size determination, standard deviation, statistical power, continuous outcomes, trial reporting
- MeSH terms
- Data Interpretation, Statistical, Humans, Randomized Controlled Trials as Topic, Sample Size
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