Question: A health researcher is interested in determining whether or not the speed at which people walk is related to their cholesterol levels. He picks 100 adult volunteers at random, checks their cholesterol levels, and then times each one while they walk a stretch of 100 yards. He is amazed at the results: a simple regression between the walk times and the cholesterol levels has an R2 of 0.98 and the slope of the regression line is 0.7. Would he be justified in concluding that walking slowly may cause high cholesterol or that high cholesterol may affect walking speed? Discuss why or why not.