Therapeutic alliance across delivery modalities: a systematic narrative review of alliance strength and outcome prediction in face-to-face, online, and blended psychotherapy

The frequency of online psychotherapy, including pure online (PO: videoconference [PO-VC], telephone [PO-TEL], asynchronous therapist-guided [PO-Async]), or blended (BLD) modalities, has grown exponentially, yet how the therapeutic alliance (TA), a key outcome predictor, compares across these formats and face-to-face (FTF) treatment remains unclear. To compare the TA strength and the TA–outcome association across FTF, PO, and BLD modalities, a systematic narrative review (Preferred Reporting Items for Systematic Reviews and Meta-Analyses/Synthesis Without Meta-analysis [PRISMA/SWiM]) was performed by searching PubMed, PsycARTICLES, and Web of Science. Studies were deemed eligible if they quantitatively compared TA across at least two modalities in adults with depressive or anxiety disorders. PO arms were classified as telepsychotherapy (PO-VC/TEL) or therapist-guided digital interventions (PO-Async). The findings were synthesized by direction and consistency. Nine studies, including three primary randomized controlled trials (RCTs) and six secondary analyses, were finally included in this study. TA strength was broadly comparable across all three modalities. One study found significantly lower patient-rated working alliance inventory (WAI) scores at Week 2 in PO-Async versus FTF, resolving by Week 8. The TA–outcome association was mixed, varying by modality, rater perspective, and timepoint. The results showed that TA was broadly equivalent across FTF, PO, and BLD formats, although asynchronous PO might show a transient week-2 lag. The TA–outcome association was less consistent in PO/BLD than in FTF. As a preliminary hypothesis, digital delivery may shift the functional emphasis of the alliance from affective bonding toward task/goal engagement.