Select the best answer to this question by checking the appropriate box.

2. Select the longitudinal study from the options below.

	A scientist examines the effect of caffeine on the athletic performance of endurance athletes. 20 experimental subjects drink coffee prior to exercise and their performance is compared to 20 control subjects who drink a placebo prior to exercise.
	A scientist investigates the relationship between vegetarianism and athletic performance by placing 2 individuals on a vegetarian diet and their examining their level of fitness.
	A scientist wants to investigate the relationship between smoking and heart rate. The heart rates of 200 individuals are measured; the heart rates of smokers and compared to those of non-smokers.
	A scientist carefully reads the scientific literature, concludes that caffeine boosts exercise performance, and writes a paper describing this conclusion.