The study showed, after a personality test,  that people identified with a house that fit our character.

Griffendors were the most extraverted, Hufflepuffs more agreeable, Ravenclaws sought more intellectual challenge, and Slytherins reported more of the “Dark Triad” personality traits: narcissism, Machiavellianism and psychopathy.

Crysel, L., Cook, C., Schember, T., & Webster, G.. “Harry Potter and the measures of personality: Extraverted Gryffindors, agreeable Hufflepuffs, clever Ravenclaws, and manipulative Slytherins” Personality and Individual Differences 2015, Volume 83, September 2015, Pages 174–179