Supplementary materials [Review] to: The Unified Narcissism Scale: Moving towards an integrated measure of narcissism

Narcissism as a psychological construct has had a contentious past both in its conceptualization and measurement. There is an emerging consensus that narcissism consists of grandiose and vulnerable subtypes, which share a common core. In the present research (N = 1002), we constructed a new measure of unified narcissism that reflects these contemporary understandings using items from the most widely used measures of grandiose and vulnerable narcissism: the Narcissistic Personality Inventory (NPI; Raskin & Terry, 1988, https://doi.org/10.1037/0022-3514.54.5.890), and the Pathological Narcissism Inventory (PNI; Pincus et al., 2009, https://doi-org/10.1037/a0016530). We used classical test theory and item response theory approaches to devise a 29-item Unified Narcissism Scale. The scale showed good internal consistency, and convergent and discriminant validity, and showed evidence of measurement invariance between men and women. This research gave strong support for the structure, reliability, and validity of the unified measure, which offers a promising avenue for further enhancing our knowledge of narcissism.