Toward Developing Clinical cut-off for the Grandiosity Scale of the Dimensional Clinical Personality Inventory 2

The present study aims to establish a clinical cut-off for the Grandiosity dimension, using item-level evaluation procedures.

Participants were 5,387 adults, including outpatients diagnosed with narcissistic personality disorder (NPD), outpatients diagnosed with other personality disorders, and adults from the community. We administered the self-reported Grandiosity scale from the Dimensional Clinical Personality Inventory 2 (IDCP-2). The equating procedure was applied to generate theta scores for participants who did not answer all items.

The Wright map revealed that outpatients scored high on the latent continuum of the Grandiosity scale. Group comparison showed large effect sizes for the mean difference between patients and non-patients. The ROC curve supports a cut off at a -0.45 score in theta standardisation, which yields a high sensitivity (91%) and moderate specificity (58%). Moreover, the PPP (71%) and NPP (79%) values suggest that the scale is able to identify NPD patients in 71% of cases, and people without NPD in 79% of cases.

The findings suggest the IDCP-2 Grandiosity scale is useful as an NPD screening tool. Possible clinical applications for the scale are described and the limitations of the study are discussed.