Effective sample size of the included studies (reflecting statistical power).

Numbers are column percentages, with absolute numbers in parentheses. For continuous outcomes, the effective sample size is the number of participants divided by the number of predictors; for dichotomous outcomes, the effective sample size is the number of participants in the smallest category divided by the number of predictors; for time-to-event outcomes, the effective sample size is the number of events divided by the number of predictors.aExcluding impact and external validation studies, because they require very different statistical power calculations.bThe number of candidate predictors was the total number of degrees of freedom (i.e., the sum of all candidate predictors, interactions, and dummy variables).