Objective: Research on nonverbal synchrony (NVS) as a core element in the therapeutic relationship has substantially increased and suggests that NVS influences therapeutic alliance and outcomes.
Method: Studies on NVS regarding body movements, vocal pitch, peripheral physiological measures, and hormonal states were included. A random-effects multilevel meta-analysis was performed on 23 publications from 13 trials.
Results: There was no significant overall association between NVS and alliance/outcome (r = .03, p = .644). Across modalities, there was a marginally significant association between higher NVS and smaller interpersonal problems (r = .10, p = .084) and a nonsignificant effect for the association between NVS and alliance (r = .06, p = .316), symptomatic outcome (r = -.06, p = .320), and other outcomes (r = .07, p = .255). There was significant heterogeneity between studies (I2 = 56.47). Moderator analyses revealed that vocal pitch synchrony was negatively associated with alliance/outcome (r = -.20, p = .011), while NVS of peripheral physiological parameters was positively correlated with alliance/outcome (r = .32, p = .006).
Conclusion: Findings suggest that specific modalities of NVS show specific associations with outcomes. More research is needed to investigate whether NVS across modalities reflects a unified underlying construct.
Keywords: alliance; meta-analysis; nonverbal synchrony; psychotherapy outcome.