Effects of treatment on outcome measures are shown in Figure 2. The analysis of PDA (transformed) through 27 months indicated no main effect for Treatment [F (2, 1616) = 0.82], a significant effect for Time [F (9, 1616) = 80.36; p < .001], and a significant Treatment X Time interaction [F (18, 1616) = 3.95; p < .02]. Analysis of post-hoc Treatment contrasts indicated that the NS condition yielded significantly greater PDA than either of the other conditions through the 27 month follow-up [Fcontrast (1, 1616) = 5.33; p < .02]. The treatment effect contrast NS v. NS+CM had a moderate effect size (average d = .28), with the NS condition yielding up to 20% more days abstinent than the other conditions at 2 years posttreatment. Levels of PDA (detransformed) by treatment condition are shown in panel A of Figure 2.
