A psychologist examines six personality tests. She suspects that four of the tests are really measuring the same personality trait and that the other two measure another personality trait. What kind of research should the psychologist conduct to test her hypothesis?

factor analysis

Explanation:

Personality tests can be explained or described as different or many tests which can involve series of standardized tasks, that can be adopted or  used to measure personality characteristics or the emotional status of people.

The factor analysis can be described as a method or technique that is used to reduce a large number of variables into fewer numbers of factors.

Its purpose is to  represent a set of variables by a smaller number.

In this case, the psychologists is expected to adopt factor analysis to test her hypothesis, this is by using smaller personality test.