Reliability and validity of a psychotic traits questionnaire (STQ)

The 'schizotypal personality' (STA) and 'borderline personality' (STB) scales of the STQ were administered to two groups: normal subjects who had completed the questionnaire on a previous occasion, four years earlier, and a 'clinical' sample, consisting of members of a self-help support group for people who at some time in the past had been psychiatrically diagnosed as suffering from a psychotic illness, mainly schizophrenia. As predicted, the latter had significantly higher scores than controls on both STQ scales, certain items also being particularly discriminating. Within the control group a test-retest analysis revealed correlations which, depending on scale and gender, were around .60. It was concluded that the STQ is a valid measure of psychotic traits and that scores on the questionnaire have good long-term stability. The results are discussed against the background, and in support of, a continuity view of psychosis.