Between-session and within-session habituation in Prolonged Exposure Therapy for posttraumatic stress disorder: a hierarchical linear modeling approach.

Prolonged Exposure Therapy is a frontline intervention for posttraumatic stress disorder, but the mechanisms underlying its efficacy are not fully understood. Previous research demonstrates that between- and within-session habituation of fear during exposure is associated with treatment outcome, but these calculations are historically performed with summary statistics such as mean subjective units of distress (SUDS). This question could be better assessed with an analytic technique that uses all SUDS measurements available within sessions. Hierarchical linear modeling was used to investigate the impact of treatment response on SUDS nested within therapy sessions nested within 14 patients. Symptom change (t=-2.43, p=.03) and responder status (t=-2.68, p=.02) predicted slope of SUDS across sessions, but did not reliably predict slope of SUDS within-session, indicating that high responders demonstrated differential between- but not within-session habituation. Thus, individuals who show greater habituation between treatment sessions may be more likely to respond to treatment.