Decline effects are rare in ecology: a meta-meta-analysis

The scientific evidence base on any given topic changes over time as more studies are published. Currently, there is widespread concern about non-random, 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 effect sizes 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 ...

任一特定研究主题的科学证据基础会随着更多研究成果的发表而随时间动态演变。当前，学界广泛担忧诸多相关主题的科学证据基础会出现随时间推移的非随机方向性变化。具体而言，若发现大效应量（例如实验组与对照组均值间存在显著差异）的研究能够快速发表，而小效应量的研究则发表周期偏长，则最终会导致平均效应量的估计值随时间推移逐渐降低，即所谓的“衰减效应（decline effect）”。若衰减效应普遍存在，则已发表的科学文献将为管理决策与未来研究资源分配提供带有偏倚且具有误导性的参考依据。我们从生态学领域的466项元分析（meta-analysis）中汇编数据，以寻找衰减效应存在的证据。研究结果显示衰减效应十分罕见，仅有约5%的生态学元分析真正出现了随时间推移的平均效应量方向性变化，其成因在于……