Predictors of outcome following psychological therapy for depression and anxiety in an urban primary care service: a naturalistic Bayesian prediction modeling approach

Background.England's primary care service for psychological therapy (Improving Access toPsychological Therapies [IAPT]) treats anxiety and depression, with a target recovery rate of50%. Identifying the characteristics of patients who achieve recovery may assist in optimizingfuture treatment. This naturalistic cohort study investigated pre-therapy characteristics as pre-dictors of recovery and improvement after IAPT therapy. Methods.In a cohort of patients attending an IAPT service in South London, we recruited263 participants and conducted a baseline interview to gather extensive pre-therapy character-istics. Bayesian prediction models and variable selection were used to identify baseline vari-ables prognostic of good clinical outcomes. Recovery (primary outcome) was defined using(IAPT) service-defined score thresholds for both depression (Patient Health Questionnaire[PHQ-9]) and anxiety (Generalized Anxiety Disorder [GAD-7]). Depression and anxiety out-comes were also evaluated as standalone (PHQ-9/GAD-7) scores after therapy. Predictionmodel performance metrics were estimated using cross-validation. Results.Predictor variables explained 26% (recovery), 37% (depression), and 31% (anxiety) ofthe variance in outcomes, respectively. Variables prognostic of recovery were lower pre-treat-ment depression severity and not meeting criteria for obsessive compulsive disorder. Post-therapy depression and anxiety severity scores were predicted by lower symptom severityand higher ratings of health-related quality of life (EuroQol questionnaire [EQ5D]) atbaseline. Conclusion.Almost a third of the variance in clinical outcomes was explained by pre-treat-ment symptom severity scores. These constructs benefit from being rapidly accessible inhealthcare services. If replicated in external samples, the early identification of patients whoare less likely to recover may facilitate earlier triage to alternative interventions.