From Diversifying Economic Quality: A Wiki for Instructors and Departments
Statistical Discrimination occurs when agents use an observable characteristic of an individual to make inferences about another attribute that is relevant to the transaction but more difficult to observe. The agents' beliefs about group averages affect their treatment of an individual member of the group. This theory is typically attributed to Kenneth Arrow's 1973 work The Theory of Discrimination and to Edmund Phelp's 1972 paper The Statistical Theory of Racism and Sexism. In Phelp's theory, the cause of inequality is an exogenous difference in the two groups' innate qualities. Without full information about different workers' productivity, the "rational" employer would make hiring decisions based on their knowledge of the applicants' group as a whole. For example, employers may be reluctant to hire and train teenage workers because their past experience with teenagers is that they only want a short-term position (e.g., a summer job). Arrow's later theory followed a similar line of thought, but did not assume that a person's or a group's traits were determined exogenously. Instead, these traits are endogenous and develop through society's beliefs about a group. For a more complete overview of statistical discrimination, read this paper, Theories of Statistical Discrimination and Affirmative Action: A Survey by Hanming Fang and Andrea Moro.
Unlike animus-based discrimination, a statistically discriminating actor's actions are not due to any direct prejudice or dislike for the disadvantaged group, but rather are meant to maximize the actor's profits. Though the actions are based on average characteristics of a group, these generalizations result in unequal outcomes for individuals who are identical except in their perceived group membership. An example is labor market discrimination against women, particularly married women, who may not be hired because they are statistically more likely to take time off to raise a family. Another example is racial profiling in law enforcement: minorities are more likely to be pulled over than white drivers.