Problems and Progress regarding Sex Bias and Omission in Neuroscience Research

Abstract

Neuroscience research has historically ignored female animals. This neglect comes in two general forms. The first is sex bias, defined as favoring one sex over another; in this case, male over female. The second is sex omission, which is the lack of reporting sex. The recognition of this phenomenon has generated fierce debate across the sciences. Here we test whether sex bias and omission are still present in the neuroscience literature, whether studies employing both males and females neglect sex as an experimental variable, and whether sex bias and omission differs between animal models and journals. To accomplish this we analyzed the largest ever number of neuroscience articles for sex bias and omission: 6,636 articles using mice or rats in 6 journals published 2010-2014. Sex omission is declining, as increasing numbers of articles report sex. Sex bias remains present and also intensifies, as increasing numbers of articles report the sole use of males. Articles using both males and females are also increasing, but few report assessing sex as an experimental variable. Sex bias and omission varies substantially by animal model and journal. These findings are essential for understanding the complex status of sex bias and omission in neuroscience research and may inform effective decisions regarding policy action.

Significance Statement Neuroscience research has historically favored the use of male over female animals, or ignored animal sex. Recognition of this sex bias and omission has spurred fierce debate and study, including new regulatory policies and scientific findings. Here we further probe this phenomenon by conducting the largest ever analysis of neuroscience research articles for sex bias and omission. We show that sex bias is still present and intensifying, and that sex omission is declining. The extent of sex bias and omission varies widely by animal model and journal. These results produce key implications for research conduct, regulatory policies, and scientific culture by revealing the still present but complex nature of sex bias and omission.