Final answer:
The Thematic Apperception Test (TAT) is a projective test used to measure the levels of need for achievement, power, and affiliation in the three-needs theory.
Step-by-step explanation:
The projective test used to measure the three needs theory, which includes the need for achievement (nAch), the need for power (nPow), and the need for affiliation (nAff), is the Thematic Apperception Test (TAT). In this test, respondents are shown a series of ambiguous pictures and are asked to write a story based on each. Trained interpreters then analyze the stories to determine levels of nAch, nPow, and nAff. The TAT aims to provide insights into an individual's social world, revealing their hopes, fears, interests, and goals, by tapping into unconscious motivations.