What Variable or Variables) Might You Use as a Basis

Essay

What variable or variables) might you use as a basis for your observations if you are interested in studying:
a. The relationship between the crime rate and unemployment in a certain city
b. Overcrowding in mental institutions
c. The relationship between smoking and health
d. Attitudes of U.S. citizens toward government-supported loans for higher education
e. The effect of rehearsal on memorization of foreign language words