Table IV. Predictive value of basic symptoms of schizophrenia in a 9.6-year follow-up of 160 young individuals.63

Table V. Positive predictive value (PPV) of basic symptoms at different levels along the pathways of mental health care with varying schizophrenia prevalences. *These figures were reported by Klosterkotter et al, 2001,63 In the other rows, the PPV has been adjusted … Thus, reports of high PPVs in schizophrenia Inhibitors,research,lifescience,medical on the basis of mental states or other risk factors can be attributed to the high baseline rates of schizophrenia in the samples used, this website created through a series of selection procedures in the sampling process34,45,46,63 or, sometimes, the statistical62 procedure used.25,66 These selection procedures contribute to exciting and clinically relevant Inhibitors,research,lifescience,medical findings. However, almost invariably a large proportion of the predictive values are

wrongly attributed to the various predictors used rather than to the selection procedures that resulted in higher prevalence or incidence rates of schizophrenia and hence a higher baseline predictive value. The consequence of this confusion is that clinicians attempting to use such findings in their practice Inhibitors,research,lifescience,medical may erroneously focus on the predictors rather than the sampling enrichment selection procedure itself. In addition, the high predictive values reported in the literature are often based on a posteriori optimization algorithms in the sample at Inhibitors,research,lifescience,medical the end of the sample enrichment filtering procedure. The correct

procedure would be to demonstrate its validity a priori in a prospective investigation at the beginning of the sample enrichment procedure. Of course, the sample enrichment strategy, similarly to the other strategies to raise the prevalence of schizophrenia that were discussed earlier, suffers from the limitation that only a tiny proportion of all detectable schizophrenia cases in the general population will be identified Inhibitors,research,lifescience,medical for early treatment in this way. The great majority of prodromal schizophrenia will never make it through the various selection procedures from the decision to visit the GP, subsequent GP referral to mental health outpatients, and from there to the specialized Ketanserin prodromal clinic- they will only come to the attention of mental health services after having developed the first acute psychotic episode, not before. Although it is true that prevention of even 1% of all transitions to schizophrenia would constitute an important result from the clinical viewpoint, one may nevertheless question whether specialized early intervention clinics can ever be made cost-effective, given competing demands for funding.67 Do people with preschizophrenia wish to be «detected»? In the previous sections, it was demonstrated that screening at the level of the general population is not useful from a methodological viewpoint, as diagnostic and predictive values would remain too low.

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