Rates of change in naturalistic psychotherapy: contrasting dose-effect and good-enough level models of change.

Most research on the dose-effect model of change has combined data across patients who vary in their total dose of treatment and has implicitly assumed that the rate of change during therapy is constant across doses. In contrast, the good-enough level model predicts that rate of change will be related to total dose of therapy. In this study, the authors evaluated these competing predictions by examining the relationship between rate of change and total dose in 4,676 psychotherapy patients who received individual psychotherapy. Patients attended 6.46 sessions on average (SD = 4.14, range = 3-29, Mdn = 5). The results indicated that although patients improved during treatment, patients' rate of change varied as a function of total dose of treatment. Small doses of treatment were related to relatively fast rates of change, whereas large doses of treatment were related to slower rates of change. Total dose had a nonlinear relationship with the likelihood of clinically significant change. Given the variability in rates of change, it appears that time limits for treatment uniform to all patients would not adequately serve patients' needs.