Fig. 2. (Top ) Mean pain scores of each combination and mean pain score of each complex of the sequential optimization procedure. Calculation of the mean pain score is described in the  Appendix. For each complex, the partition line (horizontal line) divides the “good” from the “bad” combinations. The progressive deterioration in performance of the added combinations from complex 2 onward suggests that the optimization procedure has passed the peak and is moving from the desired end point. (Bottom ) Incidence of insufficient analgesia and side effects in the complexes analyzed. Insufficient analgesia and side effects are reported as the proportion of patients in which the PCA combination had to be discontinued because of insufficient analgesia or any side effect, respectively (table 6).