Rothman KJ, Greenland S. Planning study size based on precision rather than power. Epidemiology. 2018 Jun 14.

Study size has typically been planned based on statistical power and therefore has been heavily influenced by the philosophy of statistical hypothesis testing. A worthwhile alternative is to plan study size based on precision, for example, by aiming to obtain a desired width of a confidence interval for the targeted effect. This paper presents formulas for planning the size of an epidemiologic study based on the desired precision of the basic epidemiologic effect measures.

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