However, most of the evidence for Freud's theories are taken from an unrepresentative sample. He mostly studied himself, his patients and only one child (., Little Hans ). The main problem here is that the case studies are based on studying one person in detail, and with reference to Freud, the individuals in question are most often middle aged women from Vienna (., his patients). This makes generalizations to the wider population (., the whole world) difficult. However, Freud thought this unimportant, believing in only a qualitative difference between people.