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The just-about-right pilot sample size to control the error margin

Obodo, Scholastica; Toher, Deirdre; White, Paul

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Scholastica Obodo

Paul White
Professor in Applied Statistics


In practice, the required sample size for a two-arm randomised controlled trial cannot always be determined pre-study with great accuracy. This lack of accuracy has economic, ethical and scientific implications. The sample size for a pilot study is an important consideration in helping the decision making for the sample size of a follow-on trial. Consideration of under- and over-estimation of the sample size results in the idea of a Just-About-Right (JAR) sample size. For studies involving a minimally clinical important difference (MCID) we present the pilot sample sizes to meet investigator desired JAR considerations.

Journal Article Type Article
Acceptance Date Apr 17, 2023
Online Publication Date May 23, 2023
Publication Date May 23, 2023
Deposit Date Apr 19, 2023
Publicly Available Date Sep 28, 2023
Journal International Journal of Statistics and Probability
Print ISSN 1927-7032
Electronic ISSN 1927-7040
Publisher Canadian Center of Science and Education
Peer Reviewed Peer Reviewed
Volume 12
Issue 3
Keywords Sample size, error margin, Just-About-Right, overestimation, Pilot study, power, Sample size, underestimation
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