An improvement in the method used to assess discriminatory ability when predicting the chances of a live birth after one or more complete cycles of in vitro fertilisation

d.mclernon@abdn.ac.uk Summary Our paper presents two clinical prediction models that estimate the chance of having a baby over multiple complete cycles of in vitro fertilisation (IVF)—that is, cumulative live birth.1 The pretreatment model predicts the chance of cumulative live birth before treatment starts, and the post-treatment model predicts the chance of cumulative live birth just after the first embryo transfer. Revised method The model used in our analysis was a discrete time logistic regression model. In a Cox model each patient has one linear predictor value, whereas in a discrete time logistic regression model the linear predictor varies for each discrete time point (complete cycle number).