Diagnostic categories in psychiatry may subsume considerable heterogeneity in terms of phenomenology and aetiology. For example, patients with a diagnosis of schizophrenia may differ profoundly in terms of positive or negative symptom profiles, cognitive deficit, and genetic or environmental risk factors. These natural sources of heterogeneity may be compounded by differences in treatment. Any or all of these factors may affect brain structure. Studies which simply ignore heterogeneity, or attempt to deal with it by post hoc statistical correction, may have less power to detect a group difference than studies which define cases according to refined or subdiagnostic criteria. Thus studying a sample of schizophrenic patients with high negative symptom scores and marked working memory deficits may be more likely to reveal anatomical abnormalities of frontal cortex than studying an unrefined sample of patients with schizophrenia. However, there are disadvantages to refined sampling. It is likely to be more time consuming to ascertain a sample of adequate size, and the scope of inference is reduced to the diagnostic subgroup in question.

Breaking Bulimia

Breaking Bulimia

We have all been there: turning to the refrigerator if feeling lonely or bored or indulging in seconds or thirds if strained. But if you suffer from bulimia, the from time to time urge to overeat is more like an obsession.

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