Interactive Statistics

3.13 Milk may cut the risk of kidney stones oall Source: USA Today, 1993. Doctors have always told patients with kidney stones-which contain calcium-to cut back on milk and other calcium-rich foods. But that advice may change. A new study shows men with diets high in calcium actually have a lower risk of developing kidney stones than men with low-calcium diets. Researchers at Harvard School of Public Health studied the diets of 45,619 men ages 40 to 75 who had no history of kidney stones. During the four-year study, 505 cases of kidney stones were reported. (a) Is this an observational study (and if so, which type) or is it an experiment? Explain. (b) What would the response variable and the explanatory variable be for this study? (c) Give a new theory or hypothesis stemming from these results that might be further investigated