Sample size
Estimates were made according to Riley’s recommendations for estimating sample sizes for multivariate predictive models with binary outcomes (10). Assuming 4 potential predictor variables, escalated care prevalence of 9.6% (11), proportion of unexplained variation of 0.15 (recommended by Riley in the absence of good-quality prior information), shrinkage of 0.9, marginal error in estimating the intercept of 0.05, and an acceptable difference between the apparent and adjusted R2 of 0.05, the sample size required for the development of this new model was 700 patients or 68 events.