We conducted preregistered replications of 28 classic and contemporary published findings, with protocols that were peer reviewed in advance, to examine variation in effect magnitudes across samples and settings. Each protocol was administered to approximately half of 125 samples that comprised 15,305 participants from 36 countries and territories. Using the conventional criterion of statistical significance (p < .05), we found that 15 (54%) of the replications provided evidence of a statistically significant effect in the same direction as the original finding. With a strict significance criterion (p < .0001), 14 (50%) of the replications still provided such evidence, a reflection of the extremely high-powered design. Seven (25%) of the replications yielded effect sizes larger than the original ones, and 21 (75%) yielded effect sizes smaller than the original ones. The median comparable Cohen’s ds were 0.60 for the original findings and 0.15 for the replications. The effect sizes were small (< 0.20) in 16 of the replications (57%), and 9 effects (32%) were in the direction opposite the direction of the original effect. Across settings, the Q statistic indicated significant heterogeneity in 11 (39%) of the replication effects, and most of those were among the findings with the largest overall effect sizes; only 1 effect that was near zero in the aggregate showed significant heterogeneity according to this measure. Only 1 effect had a tau value greater than .20, an indication of moderate heterogeneity. Eight others had tau values near or slightly above .10, an indication of slight heterogeneity. Moderation tests indicated that very little heterogeneity was attributable to the order in which the tasks were performed or whether the tasks were administered in lab versus online. Exploratory comparisons revealed little heterogeneity between Western, educated, industrialized, rich, and democratic (WEIRD) cultures and less WEIRD cultures (i.e., cultures with relatively high and low WEIRDness scores, respectively). Cumulatively, variability in the observed effect sizes was attributable more to the effect being studied than to the sample or setting in which it was studied.

Background: Previous randomized controlled trials have demonstrated that omega-3 polyunsaturated fatty acids (n-3 PUFA) are beneficial in reducing symptoms of depression. However, there is limited evidence regarding the influence of dietary n-3 PUFA intake on mood in adolescents drawn from population studies. Objective: In the present investigation, we examined the relationship between dietary n-3 PUFA intake on depression symptomatology in a large prospective pregnancy cohort followed for 17 years. Methods: Adolescents enrolled in the Western Australian Pregnancy Cohort (Raine) Study completed a Food Frequency Questionnaire to assess dietary fatty acid intake, as well as other dietary factors at age 14 and a fasting blood sample was taken. Participants also completed the Beck Depression Inventory for Youth (BDI-Y) at age 14 (N = 1,407) and at age 17 (N = 995). Results: An inverse relationship was observed between intake of both saturated fat and of n-3 PUFA at age 14 and BDI-Y scores at both 14 and 17 years of age. However, after adjusting for energy (kJ) intake and other lifestyle confounders, the relationships were no longer significant. Conclusions: Associations previously reported between n3 PUFA and depressive symptoms may be due to collinearity with other dietary and lifestyle factors. Depression and Anxiety, 2011.