Predictors and consequences of sudden gains in transdiagnostic cognitive-behavioural therapy for anxiety disorders.

Sudden gains-substantial stable symptom improvements between consecutive therapy sessions-are a common phenomenon. As condensed points of change, examination of sudden gains can provide insight into mechanisms of therapeutic change. This study investigated the association between sudden gains and cognitive change, therapeutic alliance, and/or client engagement in transdiagnostic group cognitive-behavioural therapy for anxiety disorders. Of 58 treatment initiators, 21% (= 12) exhibited a sudden gain. Consistent with previous research, sudden gainers demonstrated significantly greater pre- to post-treatment symptom improvement than non-sudden gainers. Observational coding of therapy sessions found that sudden gains were associated with elevated levels of cognitive change and client engagement in the pre-gain session, and elevated levels of cognitive change and therapeutic alliance in the post-gain session. However, these results varied by use of within- and between-subject control comparisons, highlighting the value using a dual control methodology. In context of previous research, the results on cognitive change replicate previous findings in depressive populations, and clarify mixed findings in anxiety populations. The results on therapeutic alliance replicate previous findings for the first time in an anxiety sample, although the between-subject control comparisons revealed complexity previously undetected. This study was also the first to investigate and thus establish the relation between client engagement and sudden gains.