What kinds of research questions or contexts might lend themselves to the use of growth curve modeling?

1. What kinds of research questions or contexts might lend themselves to the use of growth curve modeling? To the use of the regression-discontinuity design? 2. You are interested in knowing whether the particular way that personal trainers motivate the members of Gym XYZ is actually a good motivational technique (they all appear to follow the same sort of protocol), or whether it is the gym members who are innately motivated to exercise. How could you approach this research question from the perspective of a field experiment? How would this field experiment differ from a program evaluation of the same personal trainer motivational technique? Would the two research perspectives differ at all? Why or why not? As a research consultant for an evaluation firm, could you conduct a program evaluation exactly the same way as you would if you were conducting a field experiment? Why do we draw the distinction between experiments and evaluation?