Assessing Theories of State and Trait Change in Neuroticism and Symptom Improvement in the Unified Protocol

•Treatment with the UP exhibited state- and trait-level changes on neuroticism.•State-level changes occurred by session six.•Trait-level changes occurred by session twelve.•Changes in neuroticism tend to precede symptom change.•Reduction in neuroticism predicted changes in anxiety and depression. Researchers have shown neuroticism decreases with treatment (Roberts et al., 2017), although it is unclear if this reflects fleeting state-level changes (state-artifact position) or trait-level change (cause-correction hypothesis). These theories further propose that changes in neuroticism predict symptom change (cause-correction hypothesis) or are predicted by symptom change (state-artifact position). We compared these theories in a clinical trial of the Unified Protocol (UP). Participants (N = 38; Mage = 34.55, 71.1% female, 78.9% Caucasian) meeting DSM-5 criteria for a primary emotional disorder completed up to 12 weekly sessions of the UP. Neuroticism exhibited state-level changes by Session 6 but trait-level changes by Session 12. Within-person reductions in neuroticism exhibited bidirectional relations with anxiety symptom change but predicted unidirectional session-to-session reductions in depression. These findings provide relatively more nuanced support for the cause-correction hypothesis that the UP leads to trait changes in neuroticism that tend to precede symptom change.