Researchers who are trying to estimate the effects of changes in government purchases on real GDP often focus on military purchases because:
a. The types of government purchases that policymakers are likely to use to combat a recession are similar in important ways to military purchases.
b. Wars are often accompanied by price controls, which makes them particularly good times for isolating the effects of changes in government purchases.
c. Changes in military purchases are caused mainly by geopolitical developments outside the United Sates, not by other factors affecting U.S. GDP.
d. It is hard to obtain data on non-military purchases.