Department of Biological Sciences, University of Calgary, Calgary, Alberta, Canada.
Ecology. 2022 Jun;103(6):e3680. doi: 10.1002/ecy.3680. Epub 2022 Apr 13.
The scientific evidence base on any given topic changes over time as more studies are published. Currently, there is widespread concern about nonrandom, directional changes over time in the scientific evidence base associated with many topics. In particular, if studies finding large effects (e.g., large differences between treatment and control means) tend to get published quickly, while small effects tend to get published slowly, the net result will be a decrease over time in the estimated magnitude of the mean effect size, known as a "decline effect." If decline effects are common, then the published scientific literature will provide a biased and misleading guide to management decisions, and to the allocation of future research effort. We compiled data from 466 meta-analyses in ecology to look for evidence of decline effects. We found that decline effects are rare. Only ~5% of ecological meta-analyses truly exhibit a directional change in mean effect size over time arising for some reason other than random chance, usually but not always in the direction of decline. Most apparent directional changes in mean effect size over time are attributable to regression to the mean, consistent with primary studies being published in random order with respect to the effect sizes they report. Our results are good news: decline effects are the exception to the rule in ecology. Identifying and rectifying rare cases of true decline effects remains an important task, but ecologists should not overgeneralize from anecdotal reports of decline effects.
随着更多研究的发表，任何给定主题的科学证据基础都会随时间发生变化。目前，人们普遍关注与许多主题相关的科学证据基础随时间发生非随机的、有方向的变化。特别是，如果发现大效应的研究（例如，治疗和对照之间的差异较大）往往很快发表，而小效应的研究则发表较慢，那么总的结果将是随着时间的推移，平均效应大小的估计值会逐渐减少，这被称为“下降效应”。如果下降效应很常见，那么已发表的科学文献将为管理决策和未来研究工作的分配提供有偏差和误导性的指南。我们从生态学的 466 项荟萃分析中汇编了数据，以寻找下降效应的证据。我们发现下降效应很少见。只有约 5%的生态荟萃分析真正由于某种原因（通常但不总是下降的方向）随时间显示出平均效应大小的方向性变化，而不是随机变化。随着时间的推移，平均效应大小最明显的方向性变化归因于均值回归，这与主要研究按照它们报告的效应大小随机发表的情况一致。我们的结果是个好消息：在生态学中，下降效应是例外而非规则。识别和纠正真正的下降效应的罕见案例仍然是一项重要任务，但生态学家不应该从下降效应的传闻报告中过度推广。
