Rotter assessed research participants with the use of

A) physiological observations.
B) achievement tests.
C) projective tests.
D) self-report inventories.

Rotter used self-report inventories to assess research participants. One of his most well-known assessments is the Internal-External Locus of Control scale, which asks people to rate how much they believe outcomes are determined by internal factors (like their own abilities and decisions) versus external factors (like luck, chance, or powerful others). The scale is a self-report inventory because people report how they think and feel about their own beliefs, attitudes, and experiences.