Measurement of delusional ideation in the normal population: Introducing the PDI (Peters et al. Delusions Inventory)

The Peters et al. Delusions Inventory (PDI) was designed to measure delusio nal ideation in the normal population, using the Present State Examination as a template. The multidimensionality of delusions was incorporated by ass essing measures of distress, preoccupation, and conviction. Individual item s were endorsed by one in four adults on average. No sex differences were f ound, and an inverse relationship with age was obtained. Good internal cons istency was found, and its concurrent validity was confirmed by the percent ages of common variance with three scales measuring schizotypy, magical ide ation, and delusions. PDI scores up to 1 year later remained consistent, es tablishing its test-retest reliability. Psychotic inpatients had significan tly higher scores, establishing its criterion validity. The ranges of score s between the normal and deluded groups overlapped considerably, consistent with the continuity view of psychosis. The two samples were differentiated by their ratings on the distress, preoccupation, and conviction scales, co nfirming the necessity for a multidimensional analysis of delusional thinki ng. Possible avenues of research using this scale and its clinical utility are highlighted.