A meta-analytic review of randomized clinical trials of online treatments for anxiety: Inclusion/exclusion criteria, uptake, adherence, dropout, and clinical outcomes.

Over the last decade there has been rapid growth in the number of clinical trials examining internet-delivered interventions for anxiety. While there have been numerous analyses of treatment efficacy, few studies have examined treatment engagement. The current meta-analysis examined participant eligibility, uptake, adherence, and drop-out in clinical trials of internet-delivered treatments for anxiety. This meta-analysis used random effects models to obtain estimates of participant inclusion, uptake, adherence, drop-out, and within-group treatment effect size. Moderator analyses examined the effects of anxiety disorder type, treatment type, and level of clinician guidance. After screening, 140 trials with 199 treatment arms (N = 11,021) were included. An average of 46% (95% CI 42, 50) of interested people were included in the clinical trials. In the active treatment arms, 98% (95% CI 97, 99) of participants began treatment, 81% (95% CI 78, 85) of the assigned treatments were completed, 21% (95% CI 18, 23) of individuals dropped out at post-treatment based on questionnaire non-completion, and an overall within-group effect size of g = 1.03 (95% CI 0.94, 1.13) was obtained. Several moderators of interest were significant (e.g., clinical guidance, anxiety disorder type), and there was substantial heterogeneity in estimates. In conclusion, a large number of inclusion and exclusion criteria have been used in trials of internet-delivered treatments for anxiety. Once recruited into a trial, however, most people appear to begin, adhere, and complete internet-delivered treatment for anxiety. Further research exploring various eligibility criteria and their impact on engagement and efficacy is warranted.