Intraclass correlation in cluster randomized controlled trials for anxiety disorders: Evidence from a meta-analysis

Background: Cluster randomized trials (CRTs) reduce intervention contamination but may compromise statistical efficiency. Although Consolidated Standards of Reporting Trials (CONSORT) guidelines recommend reporting intraclass correlation coefficients (ICCs), compliance is limited. Aim: This meta-analysis attempts to estimate the pooled ICC of CRTs on anxiety disorders. Results: A systematic search in various databases yielded 1,124 citations, qualifying 23 studies for meta-analysis upon further screening. DerSimonian and Laird’s inverse variance method was used to calculate the pooled estimates. Among 23 studies, 16 reported ICCs at the design stage, with no significant difference compared to post-intervention values. The pooled ICC was 0.05 (95% CI: 0.04–0.06) with substantial heterogeneity; funnel plot asymmetry suggested publication bias, though Egger’s test found no small-study effects ( P = 0.913). Conclusion: Only two-thirds of CRTs on anxiety disorders complied with CONSORT recommendations on ICC reporting. The pooled ICC from this meta-analysis provides a reference for sample size estimations in future CRTs targeting anxiety disorders.