Social dominance orientation (SDO) is a personality trait which predicts social and political attitudes, and is a widely used social psychological scale. SDO is conceptualized under social dominance theory as a measure of individual differences in levels of group-based discrimination; that is, it is a measure of an individual's preference for hierarchy within any social system and the domination over lower-status groups. It is a predisposition toward anti-egalitarianism within and between groups. The concept of SDO as a measurable individual difference is a product of social dominance theory. Social dominance orientation (SDO) is a personality trait which predicts social and political attitudes, and is a widely used social psychological scale. SDO is conceptualized under social dominance theory as a measure of individual differences in levels of group-based discrimination; that is, it is a measure of an individual's preference for hierarchy within any social system and the domination over lower-status groups. It is a predisposition toward anti-egalitarianism within and between groups. The concept of SDO as a measurable individual difference is a product of social dominance theory. Individuals who score high in SDO desire to maintain and, in many cases, increase the differences between social statuses of different groups, as well as individual group members. Typically, they are dominant, driven, tough, and seekers of power. People high in SDO also prefer hierarchical group orientations. Often, people who score high in SDO adhere strongly to belief in a 'dog-eat-dog' world. It has also been found that men are generally higher than women in SDO measures. Studies have found that SDO has a strong positive relationship with authoritarian and racist beliefs. SDO was first proposed by Jim Sidanius and Felicia Pratto as part of their social dominance theory (SDT). SDO is the key measurable component of SDT that is specific to it. SDT begins with the empirical observation that surplus-producing social systems have a threefold group-based hierarchy structure: age-based, gender-based and 'arbitrary set-based', which can include race, class, sexual orientation, caste, ethnicity, religious affiliation, etc. Age-based hierarchies invariably give more power to adults and middle-age people than children and younger adults, and gender-based hierarchies invariably grant more power to one gender over others, but arbitrary-set hierarchies—though quite resilient—are truly arbitrary. SDT is based on three primary assumptions: SDO is the individual attitudinal aspect of SDT. It is influenced by group status, socialization, and temperament. In turn, it influences support for HE and HA 'legitimating myths', defined as 'values, attitudes, beliefs, causal attributions and ideologies' that in turn justify social institutions and practices that either enhance or attenuate group hierarchy. While the correlation of gender with SDO scores has been empirically measured and confirmed, the impact of temperament and socialization is less clear. Duckitt has suggested a model of attitude development for SDO, suggesting that unaffectionate socialisation in childhood causes a tough-minded attitude. According to Duckitt's model, people high in tough-minded personality are predisposed to view the world as a competitive place in which resource competition is zero-sum. A desire to compete, which fits with social dominance orientation, influences in-group and outside-group attitudes. People high in SDO also believe that hierarchies are present in all aspects of society and are more likely to agree with statements such as 'It's probably a good thing that certain groups are at the top and other groups are at the bottom'. In turn, SDO predicts stereotyping, discrimination and prejudice. SDO has been measured by a series of scales that have been refined over time, all of which contain a balance of pro- and contra-trait statements or phrases. A 7-point Likert scale is used for each item; participants rate their agreement or disagreement with the statements from 1 (strongly disagree) to 7 (strongly agree). Most of the research was conducted with the SDO-5 (a 14-point scale) and SDO-6. The SDO-7 scale is the most recent scale measuring social dominance orientation, which embeds two sub-dimensions: dominance (SDO-D) and anti-egalitarianism (SDO-E). Keying is reversed on questions 9 through 16, to control for acquiescence bias.