Generalizability and Decision Studies of a Treatment Adherence Instrument

Observational measurement of treatment adherence has long been considered the gold standard. However, little is known about either the generalizability of the scores from extant observational instruments or the sampling needed. We conducted generalizability (G) and decision (D) studies on two samples of recordings from two randomized controlled trials testing cognitive–behavioral therapy for youth anxiety in two different contexts: research versus community. Two doctoral students independently coded 543 session recordings from 52 patients treated by 13 therapists. The initial G-study demonstrated that context accounted for a disproportionately large share of variance, so we conducted G- and D-studies for the two contexts separately. Results suggested that reliable cognitive–behavioral therapy adherence studies require at least 10 sessions per patient, assuming 12 patients per therapists and two coders—a challenging threshold even in well-funded research. Implications, including the importance of evaluating alternatives to observational measurement, are discussed.