BackgroundDespite the availability of evidence-based treatments for posttraumatic stress disorder (PTSD), significant heterogeneity in the effectiveness of PTSD treatment persists, especially in community settings. Client demographics used to understand this variability in treatment outcome and dropout have yielded mixed results. Despite increasing evidence for the importance of attending to treatment engagement in community settings, few studies have explored client-level predictors.AimThe purpose of this study is to explore client-level predictors of treatment outcome and dropout beyond client demographics, and to identify client-level predictors of treatment engagement in community settings.MethodSecondary data analysis was conducted with data collected as part of an implementation-effectiveness hybrid study of cognitive processing therapy (CPT) for PTSD in a diverse community health centre. Providers (n=19) treated (n=52) clients as part of their routine clinical care. Non-demographic client-level predictors included barriers to treatment, quality of life, session-level language and employment history assessed at baseline. Treatment engagement included number of weeks in the study, number of sessions with repeated CPT content, number of unique CPT sessions attended, frequency of session attendance and consistency of session attendance.ResultsResults showed language as a significant predictor of treatment engagement. There were significant differences between Spanish and English-speaking clients, with the former having a tendency to repeat more session content than the latter (β=1.4 sessions, p=0.003), and also less likely to attend treatment frequently (r=0.62, p=0.009) and consistently (r=0.57, p=0.027) if high logistical and financial barriers were endorsed. Irrespective of language, clients who reported high quality of life at baseline were less likely to repeat CPT session content (β=−0.3, p=0.04), and those with increased baseline barriers to treatment had deceleration in PTSD symptom improvement over time (β=−0.62, p<0.05). In terms of treatment engagement moderators impacting treatment outcome, clients who repeated more session content were more likely to complete treatment (OR=1.84, p=0.037).ConclusionIdentification of client-level predictors of treatment engagement, outcome and dropout is essential to optimise treatment, particularly in community settings.