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.

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Despite the popularity of surgical repair of rotator cuff tears, literature regarding the indications for and timing of surgery are sparse. We performed a systematic review of the literature to investigate factors influencing the decision to surgically repair symptomatic, full-thickness rotator cuff tears. Specifically, how do demographic variables, duration of symptoms, timing of surgery, physical examination findings, and size of tear affect treatment outcome and indications for surgery? We reviewed the best available evidence, which offers some guidelines for surgical decision making. Variables suggest earlier surgical intervention may be needed in the setting of weakness and substantial functional disability. With regard to demographic variables, the evidence is unclear regarding their association with treatment outcome. However, older chronological age does not seem to portend a worse outcome. Pending worker's compensation claims does seem to negatively affect treatment results. Further research is required to define the indications for surgery for full thickness rotator cuff tears. However, the design and conduct of an ethical study to obtain Level I evidence on this issue will be a major challenge.

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