Fig. 3. Comparison of the positive predicted values of transfusion (probabilities are based on the score generated by the derivation set and likelihood ratios corresponding to cut points; pretest probability is the validation transfusion rate) to the observed frequency of transfusion rate in the validation set. The bars show the confidence intervals (CIs) (Wilson method) for the positive predictive values. Regression line : y, validation frequency; x, derivation frequency.