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Sample size calculations are now mandatory for many research protocols, but the ones useful in common situations are not all easily accessible. This paper outlines the ways of calculating sample sizes in two group studies for binary, ordered categorical, and continuous outcomes. Formulas and worked examples are given. Maximum power is usually achieved by having equal numbers in the two groups. However, this is not always possible and calculations for unequal group sizes are given.

Original publication

DOI

10.1136/bmj.311.7013.1145

Type

Journal article

Journal

Bmj

Publication Date

28/10/1995

Volume

311

Pages

1145 - 1148

Keywords

Data Interpretation, Statistical, Humans, Sample Size