NIH (2015), Consideration of Sex as a Biological Variable in NIH‐funded Research, National Institutes of Health, USA
NIH’s mission is to seek fundamental knowledge about the nature and behaviour of living systems and the application of that knowledge to enhance health, lengthen life, and reduce illness and disability. There is growing recognition that the quality and generalizability of biomedical research depends on the consideration of key biological variables, such as sex. NIH has long appreciated the importance of enrolling men and women in clinical research so as to provide a basis for application of results and to identify factors that affect disease course and treatment outcome. Women now account for roughly half of all participants in NIH-supported clinical research, which is subject to NIH's Policy on the Inclusion of Women in Clinical Research. However, preclinical research studies continue to rely heavily on male animals and/or omit reporting of the sex of animal subjects; this is particularly problematic in those studies intended to inform understanding of diseases and conditions affecting both sexes. Just like randomization, blinding, sample-size calculations, and other basic design elements, consideration of sex is a critical component of rigorous experimental design. Failure to account for sex as a biological variable may undermine the rigor, transparency and generalizability of research findings. The NIH expects researchers to study both male and female vertebrate animals and humans, where applicable, thereby improving our understanding of health and disease in men and women.