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The Narcissistic Personality Inventory (NPI) is the most widely used measure of narcissism in social psychological research. Although several versions of the NPI have been proposed in the literature, a forty-item forced-choice version (Raskin & Terry, 1988) is the one most commonly employed in current research. The NPI is based on the DSM-III clinical criteria for narcissistic personality disorder (NPD), although it was designed to measure these features in the general population. Thus, the NPI is often said to measure "normal" or "subclinical" (borderline) narcissism (i.e., in people who score very high on the NPI do not necessarily meet criteria for diagnosis with NPD).
Because the NPI was originally based on DSM criteria for NPD, there has been much research on its factor structure. Raskin and Terry (1988) identified seven factors of the NPI (i.e., superiority, exhibitionism, entitlement, vanity, authority, exploitativeness and self-sufficiency), mapping roughly onto the DSM criteria for NPD. Since then, several studies have further examined the factor structure of the NPI with varying results. For example, some studies report three factors; some report four factors. Furthermore, it is often the case that factors of the NPI exhibit very low internal consistency (although the full scale exhibits acceptable reliability). Thus, it may currently be concluded that the factor structure of the NPI is unknown.
Research has found that people who score high on the NPI are more likely to cheat in game-play and romantic relationships, take more resources for themselves and leave fewer resources for others, value material things and be obsessively concerned with their outter appearance.