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).