Receiver operating characteristic curves of variables predicting future anti-bradycardia pacing. For each predictor value cut-off, the sensitivity (true positive rate) is plotted against 1-specificity (false positive rate) and the points are joined to form a curve (interrupted lines). An ideal predictor would have a point passing through the top-left-hand corner of the graph, and a useless predictor would lie on the diagonal line joining the lower-left- and top-right-hand corners of the graph. An area under the curve (c statistic) of 1 indicates perfect prediction whilst an area of 0.5 indicates random predictions.¹⁶