defined as "values, attitudes, beliefs, causal attributions and ideologies" that in turn justify social institutions and practices that either enhance or attenuate group hierarchy. Legitimising myths are used by SDT to refer to widely accepted ideologies that are accepted as explaining how the world works—SDT does not have a position on the veracity, morality or rationality of these beliefs, as the theory is intended to be a descriptive account of group-based inequality rather than a normative theory. Early development 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". Scale 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). SDO-7 items Dominance Sub-Scale Some groups of people must be kept in their place. It's probably a good thing that certain groups are at the top and other groups are at the bottom. An ideal society requires some groups to be on top and others to be on the bottom. Some groups of people are simply inferior to other groups. Groups at the bottom are just as deserving as groups at the top. (reverse-scored) No one group should dominate in society. (reverse-scored) Groups at the bottom should not have to stay in their place. (reverse-scored) Group dominance is a poor principle. (reverse-scored) Anti-Egalitarianism Sub-Scale