Rothman KJ, Greenland S. Planning study size based on precision rather than power. Epidemiology. 2018 Sep;29(5):599-603.

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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