Starting with his 1947 essay "Wagner, Nietzsche and Hitler", Adorno produced a series of influential works to describe psychological fascist traits. One of these works was "The Authoritarian Personality" (1950), published as a contribution to the "Studies in Prejudice" performed by multiple research institutes in the US, and consisting of 'qualitative interpretations' that uncovered the authoritarian character of test persons through indirect questions. The books have had a major influence on sociology and remain highly discussed and debated. In 1951 he continued on the topic with his essay "Freudian Theory and the Pattern of Fascist Propaganda", in which he said that "Psychological dispositions do not actually cause fascism; rather, fascism defines a psychological area which can be successfully exploited by the forces which promote it for entirely non-psychological reasons of self-interest."