The deviant case analysis (Robinson, 1976) is an extension of theevaluative case study discussed earlier Here cases of deviant and normal individualsare compared for significant differences. These differences may have important implications for the etiology or origin of the psychopathology in question. Mednick and his colleagues have used this procedure to study the etiology of schizophrenia(Mednick1969. Mednick,schulsinger& Venables,1981).Theyfound, for that the autonomic systems of normal and schizophrenic children function differently someday it may be possible to use to predict which will become schizophrenic. Clearly the case study is a useful source of information It is especially useful when we cannot experiment because of practical or ethical reasons.(obviously we would not subject an individual to a stressful life experience such as loss of a parent, simply to observe the outcome) However, this approach has several limitations.First,working with only one or perhaps a few subjects, we cannot be sure the people we are evaluating are representative of the general population; we would obtain a very distorted picture of language development if we studied exceptional child. Second, if we are not able to observe an individual directly all the time, we cannot be sure that we are aware of all the relevant aspects of that person's life.Third, subjects or others providing data for case studies might neglect to mention important information, either because they believe it is irrelevant or because they find it embarrassing. An even more severe problem is that case studies frequently rely on retrospective data. Retrospective data are data collected in the present that are based on recollections of past events. Information collected long after the fact is apt to be inaccurate for several reasons. People often cannot accurately remember all that happened at a particular point in time. We also know that human memories become altered reconstructed over time by the cognitive system. Retrospective data can also be easily biased by the situation in which the data are collected. The mood of the data provider example, will affect recollections; we tend to recall more positive events when we are in a good mood and more negative events when we are in a bad mood In addition, aspects of the situation can trigger particular kinds of recollections.Something that seems as innocuous as a of da Vinci's Mona Lisa on a therapists wall might bring to mind past experiences with enigmatic, dark-haired women that otherwise would not have been recalled at all.Even unintended hints from a researcher that certain kinds of are more interesting than others can bias the kind of information that is brought to mind. For these reasons, reliance on retrospective data is a shortcoming. Records made at the time of an event are always much preferred. The use of retrospective data is not limited to case studies but frequently occurs in this research method. Finally,because we have not created the antecedent conditions in case studies, we cannot make cause and effect statements about the