Carl Iver Hovland (June 12, 1912 – April 16, 1961) was a psychologist working primarily at Yale University and for the US Army during World War II who studied attitude change and persuasion. He first reported the sleeper effect after studying the effects of the Frank Capra's propaganda film Why We Fight on soldiers in the Army. In later studies on this subject, Hovland collaborated with Irving Janis who would later become famous for his theory of groupthink. Hovland also developed social judgment theory of attitude change. Carl Hovland thought that the ability of someone to resist persuasion by a certain group depended on your degree of belonging to the group.