Equivalence of Narcissistic Personality Inventory constructs and correlates across scoring approaches and response formats

• The effects of scoring and response formats on the validity of the NPI were tested.
• We tested the equivalence of narcissism facets and correlates.
• Results were robust across scoring methods and response formats for vanity and leadership.
• The entitlement facet was not equivalent across scoring methods and response formats.

The prevalent scoring practice for the Narcissistic Personality Inventory (NPI) ignores the forced-choice nature of the items. The aim of this study was to investigate whether findings based on NPI scores reported in previous research can be confirmed when the forced-choice nature of the NPI’s original response format is appropriately modeled, and when NPI items are presented in different response formats (true/false or rating scale). The relationships between NPI facets and various criteria were robust across scoring approaches (mean score vs. model-based), but were only partly robust across response formats. In addition, the scoring approaches and response formats achieved equivalent measurements of the vanity facet and in part of the leadership facet, but differed with respect to the entitlement facet.