Figure 3. Mean 24-h pruritus score for each group (mean, +/− SD). Groups were significantly different (analysis of variance, P = 0.003). Dotted line represents trend toward higher pruritus score with increasing dose (linear regression analysis, P = 0.001); the model predicts an increase of 0.6 (95% CI, 0.23-0.98) for each increase in intrathecal morphine dose of 0.1 mg.