Of course, it is possible for too large of an increase to put pressure on real interest rates, thereby crowding out potential private investment. If there is significant exchange-rate risk, such as in non-reserve currency countries, that, too, should be taken into account.
在许多国家，你可以务实地预期相当于GDP的一个百分点的增量投资可以带来4%的平均回报。如果边际实际利率为1%，那么公共投资的增加实际上可以减少未来债务负担。当然，有可能增量太大以至于对实际利率产生压力，从而挤出潜在私人投资。如果存在重大汇率风险，比如对于非储备货币国家，那么这一点也应该考虑在内。