Although publication bias is the obvious explanation for these otherwise counterintuitive findings, systematic differences between smaller and larger studies may also play a role. For example, Caspi et al. (1) and Lotrich and Lenze (22) argued that smaller cG×E studies tend to use higher-precision prospective measures, whereas larger studies tend to use lower-precision retrospective reports. If so, smaller replication studies may be more likely to be positive because they tend to analyze variables with less measurement error than larger replication studies and not because of publication bias. However, this argument does not explain why negative replications are published alongside novel cG×E findings more often than positive replications or why negative replications published alone have the largest sample sizes. Taken together, we believe that publication bias among replication attempts is the most parsimonious explanation for our results.
