Gender "in the wild": toward a person-specific behavioral neuroendocrinology.

Sex- and gender-related contributions to behavior "in the wild", as observed in humans in the natural context of their daily lives, can vary strikingly across individuals and be highly enmeshed - so much so that it is impossible to determine whether an average difference between women and men, for instance, reflects biological or sociocultural factors, respectively. Indeed, empirical insights may not just be limited, but may even be distorted, if study designs and data analyses continue to place unique people in ill-assumed homogenous groups for mean-based calculations. Findings may ultimately generalize to no one. An idiographic, or personalized, approach, however, reveals the intricate ways in which sex-related characteristics, such as gonadal hormones, and gender-related experiences combine to matter for behavior. This approach often requires novel data, that is, many repeated observations from the same people on the same variables, and time series analyses. The goal of this article is to briefly review perspectives on sex and gender in research, and then to illustrate how sex- and gender-related factors can be studied together in unique individuals using an idiographic approach. Specifically, person-specific analyses of data from select participants in three different intensive longitudinal studies with 75 or 100 assessment days will showcase unique relations between sex-related neuroendocrinology (i.e., menopause, oral contraceptive use, and puberty) and gender-related self-concepts (i.e., perceptions of masculinity and femininity), or demonstrate links with cognition or mental health. These illustrations will highlight the importance of leveraging methodological innovation to study the individualization of sex and gender, and the necessity of decreasing reliance on sex- and gender-linked assumptions of homogeneity in human neuroendocrine research.