6. A study was designed to examine the effect a person's level of education (high school diploma, 2-year college degree, 4-year college degree, and graduate/advanced de- gree) has on his or her career happiness. The study involved a random selection of people working in the aviation industry, including airline ticket agents, security officers, baggage handlers, and pilots. A person's career happiness was defined as scores on the Career Happiness Rating Scale and could range from 40 to 200; the higher the score, the happier the individual. The statistical procedure the researcher used to measure this effect was

a. factorial ANOVA.

b. t test for independent sample means.

c. single-factor ANOVA.

d. correlation.