Abstract
One of the most widely used measures of psychosis-related symptoms and characteristics is the 74-item Schizotypal Personality Questionnaire (SPQ). Using multidimensional Item Response Theory (bifactor 2-parameter model), we calibrated SPQ items in a sample of 375 youths aged 9-24 years and constructed a fully functional computerized adaptive form of the SPQ on an open-source platform for public use. To assess validity, we used the above parameters to simulate CAT sessions in a separate validation sample (N = 100) using three test-length-based stopping rules: 8 items, 16 items, and 32 items. Those scores were then compared to full-form and SPQ-Brief scores on their abilities to predict psychosis or clinical risk status. Areas under the receiver operating characteristic curves indicated mediocre predictive ability, but did not differ among any of the forms, even when only eight adaptive items were administered. The Youden index for the 16-item adaptive version was higher than that for the 22-item SPQ-Brief. Classification accuracy for the full SPQ was 73% compared to 66% for the both the SPQ-Brief and adaptive versions (average of three stopping rules). The SPQ-CAT shows promise as a much shorter but valid assessment of schizotypy which can save time with minimal loss of information.