A 10-year follow-up study of sex inclusion in the biological sciences

Abstract

In 2016, to address the historical overrepresentation of male subjects in biomedical research, the US National Institutes of Health implemented a policy requiring investigators to consider sex as a biological variable. In order to assess the impact of this policy, we conducted a bibliometric analysis across nine biological disciplines for papers published in 34 journals in 2019, and compared our results with those of a similar study carried out by Beery and Zucker in 2009. There was a significant increase in the proportion of studies that included both sexes across all nine disciplines, but in eight of the disciplines there was no change in the proportion studies that included data analyzed by sex. The majority of studies failed to provide rationale for single-sex studies or the lack of sex-based analyses, and those that did relied on misconceptions surrounding the hormonal variability of females. Together, these data demonstrate that while sex-inclusive research practices are more commonplace, there are still gaps in analyses and reporting of data by sex in many biological disciplines.

Keywords: human biology; medicine; meta-analysis; meta-research; none; sex bias; sex differences; sex inclusion.

Figure 1.. Comparison of studies by field, sex, and sex-based analyses in 2009 and 2019.

(A). The proportion of articles surveyed in 2009 and 2019 which utilized male subjects, female subjects, both male and female subjects, or those that did not specify the sex of the subjects. Data are presented by individual biological discipline as well as by the sum of all nine disciplines. (B). The percentage of articles surveyed in 2009 and 2019 which utilized both male and female subjects and conducted sex-based analyses, either by including sex as a covariate or by subgroup analyses. Data are presented by individual biological discipline as well as by the sum of all nine disciplines. The source data for this figure are in Supplementary file 1.

Figure 2.. Percent of articles which provided the sample size (n) by sex, rationale for single-sex studies, or rationale for the lack of sex-based analyses.

(A). The percentage of articles which utilized both male and female subjects and provided a description of the sample size by sex. Data are presented by individual biological discipline as well as by the sum of all nine disciplines. (B). Categorization of articles which provided rationale for single sex-studies or the lack of sex-based analyses (n = 30) into seven distinct themes. Each theme includes representative rationale derived from the experimental methods. The source data for this figure are in Supplementary file 1.