Question

A researcher working with college-age football players is conducting a longitudinal study to examine an athlete's decline in on-the-field performance as the athlete ages. What type of development would the researcher most likely be studying?

Answer 1

I believe the answer is: physical development

In longitudinal study same subjects over a certain period of time.  From the study above, we can see that on-field-performance is the dependent variables. Since there is no way for the researchers to conduct and proof the psychological development, physical development ia the most suitable choice.