Weinberg, Fleisher, and Hashimoto (2007) studied almost 50,000 students' evaluations of their professors in almost 400 economics courses at The Ohio State University over a 10-year period. For each of their findings, outlined below, state (i) the independent variable or variables, and their levels where appropriate, (ii) the dependent variable(s), and (iii) what category of research design is being used:

I-scale independent variable(s) and scale dependent variable

II-nominal independent variable(s) and scale dependent variable

III-only nominal variables

Explain your answer to part (iii).

a. The researchers found that students' ratings of their professors were predictive of grades in the class for which the professor was evaluated.

b. The researchers also found that students' ratings of their professors were not predictive of grades for other, related future classes. (The researchers stated that these first two findings suggest that student ratings of professors are tied to their current grades but not to learning-which would affect future grades.)

c. The researchers found that male professors received statistically significantly higher student ratings, on average, than did female professors.

d. The researchers reported, however, that average levels of students learning (as assessed by grades in related future classes) were not statistically significantly different for those who had male and those who had female professors.

e. The researchers might have been interested in whether there were proportionally more female professors teaching upper-level than lower-level courses and proportionally more male professors teaching lower-level than upper-level courses (perhaps a reason for the lower average ratings of female professors).

f. The researchers found no statistically significant differences in average student evaluations among nontenure-track lecturers, graduate student teaching associates, and tenure-track faculty members.