To answer the following questions, researchers would measure two variables for each individual unit in the study. In each case, specify the two variables, and the variable type for each. Then, specify which is the explanatory variable and which is the response variable.
a. For college students, is there a relationship between grade point average (GPA) and average number of hours spent studying each week?
b. Individuals in the United States fall into one of a small number of tax brackets based on level of income. Is there a relationship between a person's tax bracket and the percent of income donated to charities?