Sex and Gender Differences Research Design for Basic, Clinical, and Population Studies: Essentials for Investigators.

For example, in a study in which the exposure–disease association approaches statistical significance (say, a 2 standard error difference in outcome between study arms), splitting subjects into two groups of similar size will yield a one in three chance that the association will be sizeable and statistically significant ( P < 0.05) in one group and inconsequential in the other (less than a standard error difference) ( 77 ).

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