Many traits correlate with body size. Studies that seek to uncover the ecological factors that drive evolutionary responses in traits typically examine these responses relative to associated changes in body size using multiple regression analysis. However, it is not well appreciated that in the presence of strongly correlated variables, the partial (i.e., relative) regression coefficients often change sign compared to the original coefficients. Such sign reversals are difficult to interpret in a biologically meaningful way, and could lead to erroneous evolutionary inferences if the true mechanism underlying the sign reversal differed from the proposed mechanism. Here, we use simulations to demonstrate that sign reversal occurs over a wide range of parameter values common in the biological sciences. Further, as a case‐in‐point, we review the literature on brain size evolution; a field that explores how ecological traits relate to the evolution of relative brain size (brain size relative to body size). We find that most studies show sign reversals and thus that the inferences of many studies in this field may be inconclusive. Finally, we propose some approaches to mitigating this issue.

中文翻译：

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控制体重会导致生物学中的推断偏见

许多特征与体型有关。试图揭示驱动性状进化反应的生态因素的研究通常使用多元回归分析来检查这些反应与体型相关变化的关系。但是，没有很好的认识到，在存在强相关变量的情况下，与原始系数相比，部分（即相对）回归系数经常会改变符号。如果符号反转的真实机制与所提出的机制不同，则这种符号反转很难以生物学上有意义的方式进行解释，并且可能导致错误的进化推论。在这里，我们使用模拟来证明符号反转发生在生物学中常见的各种参数值上。此外，举例来说，我们回顾了有关大脑大小进化的文献；研究生态特征如何与相对大脑大小（大脑大小相对于身体大小）的演变相关的领域。我们发现大多数研究都显示出符号反转，因此，该领域中许多研究的推论可能尚无定论。最后，我们提出了一些缓解此问题的方法。