Background: Several self-report instruments were developed to capture psychotic prodrome, and were claimed to have good predictive validity. The feasibility of screening is questionable considering the heterogeneity of the targeted populations and the negative ramifications of false positive identification. This study developed a questionnaire using data covering a wide range of clinical characteristics.
Methods: One hundred and eleven putative pre-psychotic participants, 129 normal comparison subjects, and 95 non-psychotic psychiatric outpatients completed a 231-item questionnaire comprising a 110-item Wisconsin psychotic prone scale, 74-item schizotypal personality questionnaire, 33-item basic symptoms, and 14-item cognitive symptoms. Items showing the best discriminating power, estimated using chi-square statistics with Bonferroni correction, were extracted to create a brief version. A two-stage cut-off approach emphasizing specific items was applied to maximize sensitivity and specificity. The concurrent validity of the proposed approach was estimated using a ten-fold cross-validation procedure.
Results: A 15-item self-report questionnaire was developed. Respondents checking at least eight items, or those checking three to seven items including any of the three referring to feeling stress in crowds, aloofness, and perceptual disturbance, would be considered putatively pre-psychotic with the largest sensitivity+specificity (0.784+0.705=1.489). This cut-off selection was the best estimate by calculating 1000 permutations in the cross-validation procedure.
Conclusions: This investigation proposes a different orientation for applying questionnaires to screen putative pre-psychotic states, with less emphasis on attenuated psychotic symptoms and predictive values. Besides providing a handy tool for increasing awareness and referral, the instructions of such a screening questionnaire should be carefully worded.
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