CIs that crossed the line of equivalence indicated that the true RR may be 1 rather than the calculated value. The χ2 test was used to calculate the percentage variation across studies caused by their heterogeneity. Significance for this test was set liberally at p ≤ 0.1, since in practice, the test often lacks the power to detect interstudy differences of the treatment effect.16 DerSimonian and Laird’s random effects model of pooling17 was used to provide a more conservative estimate of the true effect. These analyses were carried out with Review Manager 4.2 (Cochrane Collaboration, Oxford).