Gerontologists interested in the effects of aging on reaction time have two groups of subjects take a test in which they must indicate as quickly as possible whether a probe word was a member of a previous set of words. One group of subjects is between the ages of 25 and 45, and the other group is between the ages of 65 and 85. The time it takes to make the response is measured.
a. What is the independent variable in this study?
b. What is the dependent variable in this study?
c. Identify the control and experimental groups in this study.
d. Is the independent variable manipulated, or is it a subject variable?