When researchers study sex or gender differences in health outcomes they often find significant disparities. But what do sex or gender actually mean and measure? The simplest answer is to consider that all subjects are either women or men and to group them accordingly. Historically differences between the women and men were thought to arise from biology, reproductive organs, hormones or biological processes. This is what the term 'sex' generally means. The division between sex and gender in social science research developed in the 1960s. The split highlighted the need to move beyond a narrow focus on biology and recognize that socioeconomic conditions and cultural norms also shape and constrain education, career choices, salaries, and health. The term, gender refers to social aspects of being a man and woman, features that are formed in relation to upbringing, conditions in daily life, norms and culture.