Four Personality Types (IMAGE) Northwestern University Caption Northwestern University researchers have sifted through data from more than 1.5 million questionnaire respondents and found at least four distinct clusters of personality types. Credit Northwestern University Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.