Answer: Case studies
Explanation: Sigmund Freud was an Austrian psychoanalyst founder of psycho dynamic in psychology, by which the unconscious in the mind inclines to certain behaviour. Humans, according to Freud, are only those who participate in the so-called "drama" caused by the subconscious desires of our mind as well as by coincidence combined with the conscious part of our mind. In this regard, sexual and psycho sexual development is very important that Freud studied in his patients.
As a psychoanalyst and psychotherapist, Freud cared for his patients and from the treatment he came to many conclusions that he had drawn into theories. Based on his daily conversations with patients, which are in case studies, he finds his insights on the functioning of the human mind, and especially the subconscious, which Freud claimed to have triggered many things. Case studies are, therefore, many of the cases of his patients that Freud talked to and subsequently published.