Figure 2. (Top) Two graphs depicting pooled visual analog pain intensity versus pain relief scores recorded before (left) and after (right) maximum analgesia in the methadone study. The slope of the linear regression line characterizing pooled data before (-2.16 +/- 0.57; 95% confidence interval) and after (-1.05 +/- 0.1) maximum analgesia changed significantly. Individual slopes uniformly were significantly steeper before than after maximum analgesia (P < 0.01; inset). The relationship between pain intensity and pain relief scores before and after maximum analgesia had changed systematically. (Bottom) Two graphs depicting pooled visual analog pain intensity versus pain relief scores recorded before (left) and after (right) maximum analgesia in the hydromorphone study. The slope of the linear regression line characterizing pooled data before (-1.47 +/- 0.26; 95% confidence interval) and after (-1.09 +/- 0.07) maximum analgesia changed significantly. Individual slopes uniformly were steeper before than after maximum analgesia (P < 0.01; inset) with one exception. The relationship between pain intensity and pain relief scores before and after maximum analgesia had changed systematically.