Freud relied upon an idiographic approach to develop his ideas, using a small number of case studies eg Little Hans. Critics have suggested that it is not possible to make universal claims about human nature based on such a limited sample. Although Freud's observations were detailed and carefully recorded, his interpretations were highly subjective and it is unlikely any other researcher would have drawn the same conclusions. Therefore in comparison with approaches eg Behaviourism, his methods lacked scientific rigour.