At the time it was first proposed, conflict theory was considered outside the mainstream of more established criminological theories, such as strain theory, social disorganization theory and differential association theory. Barbara D. Warner, associate professor of criminal justice and police studies at Eastern Kentucky University, notes that conflict theory has been the subject of increasing criticism in recent years. Recent studies claim that, while there may have been real sentencing differences related to non-legal characteristics such as race in the 1960s, sentencing discrimination as described by the conflict theorists at that time no longer exists. Criticism has also pointed to the lack of testability of the general theory. While much research has been done to correlate race, income level and crime "frequency", typically of less serious criminal behavior such as theft or larceny, research has shown there to be no significant correlation between race, income level and crime "seriousness". Thus, conflict theory encounters difficulties in attempting to account for the high levels of violent crime such as murder, homicide and rape, in minority populations.