Nine studies were included for the review (n=237): one randomised controlled trial (RCT) (n=28) and eight quasi-experimental studies (n=209). Samples sizes ranged from 14 to 61 participants.
EIBI was associated with a large positive effect on full scale IQ (Hedge's g 1.10, 95% CI 0.87 to 1.34; 10 comparisons, n=237) and a moderate positive effect on adaptive behaviour (Hedge's g 0.66, 95% CI 0.41 to 0.90; eight comparisons, n=178).
Sensitivity analysis that included only the comparison group from the study with two non-intervention groups did not significantly alter the findings. There was no evidence of significant statistical heterogeneity or publication bias.