Paul Costa Jr.

If you ask a psych major how to measure personality, they'd probably point you to the Big Five model, which is similar to MBTI, but it has been proven to have predictive power.

The Big Five is a statistical model created by Robert McCrae and Paul Costa.

These researchers took every adjective describing people that they could find and subjected them to factor analysis, which basically involves statistically determining the similarity between them.

So using this, they reduced these adjectives to five factors, which each exist on a continuum.