Questions, answers, and metadata collected from 11,243 Narcissistic Personality Inventories. The data was hosted on OpenPsychometrics.org a nonprofit effort to educate the public about psychology and to collect data for psychological research. Their notes on the data collected in the codebook.txt
From Wikipedia:
The Narcissistic Personality Inventory (NPI) was developed in 1979 by Raskin and Hall, and since then, has become one of the most widely utilized personality measures for non-clinical levels of the trait narcissism. Since its initial development, the NPI has evolved from 220 items to the more commonly employed NPI-40 (1984) and NPI-16 (2006), as well as the novel NPI-1 inventory (2014). Derived from the DSM-III criteria for Narcissistic Personality Disorder (NPD), the NPI has been employed heavily by personality and social psychology researchers.
The NPI is not intended for use in diagnosing Narcissistic Personality Disorder. Rather, it 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 all criteria for diagnosis with NPD).