Despite Freud primarily regarding himself as a scientist, the definition of science of Freud somewhat varies by the traditional notion of modern psychologists. Freud's reliance is increasingly on deductive reasoning as opposed to rigorous methods of research, and his observations are subjective, corresponding to a relatively minimal sample of patients mostly comprising the upper and upper-middle classes. Freud does not make observations under controlled conditions nor does he quantify his data. Freud almost exclusively makes use of the case study approach, formulating his hypotheses after the facts of a case become apparent.