Model discrimination

Discrimination refers to the ability of the CPM to distinguish patients who develop delirium from those who do not develop delirium. Model discrimination is expressed as the area under the receiver operating characteristic curve, or ‘c-index’, which plots the sensitivity (true-positive rate) against 1−specificity (false-positive rate) for consecutive cut-offs of the predicted risk. Perfect discrimination gives a c-index of 1, and no discrimination (no better than the toss of a coin) results in a c-index of 0.50. Prediction models with c-indices between 0.9 and 0.99 are considered to have excellent discrimination, 0.8 and 0.89 good discrimination, 0.7 and 0.79 fair discrimination and 0.51 and 0.69 poor discrimination.¹¹