Twenty-eight comparative studies (n=3,461), 10 of which were cohort studies, were included in the review. Sample sizes varied between 15 and 480. CTAM scores varied between 27 and 89 with a mean score of 55.72 (SD 15.00). Further details of the individual study scores and assessment criteria were not reported. A significant association between poorer study quality and larger effect sizes was reported using meta-regression.
A overall significant Hedge's g effect size in favour of cognitive therapy in comparison with control was reported (-0.59; 95% -0.811, -0.371; z=-5.26, p<0.0001; 25 studies). Subgroup analyses reported that data for adults were statistically significant (combined Hedge's g -0.775; 95% CI: -1.051, -0.498; z=-5.497; p<0.0001; 18 studies) and data for adolescents were not significant. Other subgroup analyses were reported in the review, but some included only small numbers of studies and most showed that subgroups were associated with significant effect sizes.
In all of the analyses performed, publication bias was evident in one or more of the various statistical tests performed.