How much therapy is enough? Comparing dose-effect and good-enough models in two different settings.

The Dose-Effect model holds that longer therapy leads to better outcome, although increasing treatment length will yield diminishing returns, as additional sessions lead to progressively less change in a negatively accelerating fashion. In contrast, the Good-Enough-Level (GEL) model proposes that patients, therapists, or patients-with-therapists decide on ending treatment when treatment outcome is satisfactory, meaning that patients who change faster will have shorter treatments. If true, this means that aggregating among patients with different treatment lengths would yield biased results. Most previous research has shown that symptom change rate depends on treatment length, but all of these studies used data from University counseling centers in the United States. There is a need to test if previous results hold in different settings. Two datasets from Swedish community-based primary care (n = 640) and psychiatric care (n = 284) were used. Patients made session-wise ratings on the Clinical Outcomes in Routine Evaluation-Outcome Measure (CORE-OM). Multilevel models indicated better fit for a model in which treatment length moderated symptom change rate. In the primary care sample, patients in longer treatments achieved more symptom change from pre- to posttreatment, despite having slower rate of improvement. The most important aspect of the GEL model was supported, and no evidence was found for a negatively accelerating Dose-Effect curve. Results cannot be generalized beyond about 12 sessions, due to scarcity of data for longer treatments.