Thirty-one RCTs (2,442 participants) were included in the review. Quality of the RCTs was variable: 12 did not report randomisation method, 14 did not report allocation concealment and none provided sufficient detail to be free of selective reporting.
Waiting list versus self-help: Compared with waiting list, there was a statistically significantly greater reduction in anxiety symptoms with self-help interventions (SMD -0.88, 95% CI -1.05 to-0.71; 20 studies, Ι²=44%). There was a slight discrepancy in the figures reported in the text and forest plot and we used the forest plot figure. Analyses restricted to studies of guided self-help interventions showed greater efficacy (SMD -0.97, 95% CI -1.17 to -0.76; 12 studies), as did analyses considering only web-based and multimedia self-help interventions (SMD -0.90, 95% CI -1.13 to -0.68; 13 studies). In terms of drop-out, there was a significant difference in favour of the waiting-list condition (OR 1.98, 95% CI 1.26 to 3.11; 20 studies).
Therapist administered treatment versus self-help: There was a significant difference between self-help and therapist-administered psychological therapy in favour of therapist-administered treatment (SMD 0.34, 95% CI 0.03 to 0.65; 12 studies, Ι²=72%). Removing pure self-help interventions from the analysis resulted in there being no significant difference between guided self-help and therapist-administered treatment. An analysis of only web-based and multimedia interventions showed no significant difference between self-help and therapist-administered psychological therapy in terms of anxiety symptoms or drop-out rates.
Subgroup analyses indicated that self-help interventions were effective in the treatment of panic disorder and social phobia, although three RCTs showed outcomes in favour of control for mixed anxiety disorders. Other results were presented in the review. None of the RCTs assessed acceptability. Publication bias was not detected.