The present review introduces the notion of statistical power and the hazard of under-powered studies. The problem of how to calculate an ideal sample size is also discussed within the context of factors that affect power, and specific methods for the calculation of sample size are presented for two common scenarios, along with extensions to the simplest case.
Whitley et al. (2002) reported a review. Sample size calculations must be performed at the design stage of clinical studies to ensure adequate statistical power and prevent falsely concluding an absence of effect.
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