One criticism of meta-analyses is that positive studies may be more likely to be published than negative studies and this sort of publication bias can create false positive results. We thus determine how many unpublished studies would need to exist to make the result of our overall analysis non-significant (p=0.05). We found that 729 unpublished or undiscovered studies with an average sample size (N = 755) and a non-significant result (p = 0.5) would need to exist. This corresponds to a fail-safe ratio of 14 studies not included in this meta-analysis for every included study.
