Assessing the presence of selection bias in meta-analyses of randomised trials using baseline heterogeneity

Results Five of the 12 meta-analyses exhibited heterogeneity (I >0.30) in age differences, when there should have been none, with two having significant or substantial heterogeneity (I > 0.50). In three meta-analyses we found that the age of intervention group was statistically significantly higher than in the control group. Two meta-analysis had a distribution of p-values that were inconsistent with chance. Meta-regression explained some of the observed heterogeneity in two meta-analyses as a consequence of poor allocation concealment. Conclusions The majority of a sample of recent meta-analyses showed that there were signs of imbalance and or heterogeneity in ages between treatment groups, when there should have been none. Systematic reviewers might consider using the techniques described here to assess the validity of their findings.