Which of the following is NOT an example of an operational definition of a psychological construct?
a. A child psychologist administers an intelligence test to assess the cognitive development of children
b. A manager has her employees complete a personality inventory to measure their levels of extraversion and other traits
c. A researcher argues that, theoretically, there are three completely different “types” of happiness
d. An educational psychologist gathers high school GPA scores to serve as a measurement of school performance