Academic research indicates that the over-representation of some racial minorities in the criminal justice system can in part be explained by socioeconomic factors, such as poverty, exposure to poor neighborhoods, poor access to public education, poor access to early childhood education, and exposure to harmful chemicals (such as lead) and pollution. Racial housing segregation has also been linked to racial disparities in crime rates, as blacks have historically and to the present been prevented from moving into prosperous low-crime areas through actions of the government (such as redlining) and private actors. Various explanations within criminology have been proposed for racial disparities in crime rates, including conflict theory, strain theory, general strain theory, social disorganization theory, macrostructural opportunity theory, social control theory, and subcultural theory.