Empirical Testing of Conrads and Docherty et als Models

We applied the structural equation modelling technique (SEM) to test the internal validity of Conrad's and Docherty et al.'s stage models. As latent variables we chose the symptoms and symptom patterns subsumed under the stages and the stages as such [23]. We also tested external validity, i.e. to what extent the two models tallied with each other and with empirical data on the early course of schizophrenia collected retrospectively using the Interview for the Retrospective Assessment of the Onset of Schizophrenia (IRAOS) [24-28] in a representative sample of first illness episodes of schizophrenia (n = 232) from the Age, Beginning, Course (ABC) Schizophrenia Study. Our analysis is based on a subsample of 170 patients who had experienced a clear-cut prepsychotic prodromal stage (73% of 232).

Neither of the two models was significantly supported or even converged in the analysis of internal and external validity or in the comparisons with the empirical data. Conrad's model explained 74% (goodness of fit: 0.79, adjusted 0.74) and Docherty et al.'s model 71% (goodness of fit: 0.75, adjusted 0.71) of the empirical data, thus failing to attain the conventional level of goodness of fit of >90% [23].

This result is no surprise. The reasons lie not only in the construction weaknesses of these models, but also in the partly imprecise description of the symptoms and their occurrence at the stages.

Because of the difficulties posed by a comprehensive validation, we had earlier compared the sequence of symptom onset over time as an indicator of the sequence of stages in Conrad's model with a slightly different set of the IRAOS data from the ABC study [29]. The results confirmed Conrad's model only with respect to prepsychotic ''trema'' as the first stage of illness (this was the case in 76% of the first-admission sample, of whom 84% were first illness episodes and of these first-episode cases 73% had experienced a prepsychotic prodromal stage). But the comparison failed to provide any evidence for the sequence of the other stages. To conclude, Conrad's model provides a correct representation only of the distinction between a prepsychotic prodromal stage, which he called ''trema'', and the subsequent stage of psychosis.

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