My Berkeley colleagues David and Christina Romer, for example, faced an analogous problem when seeking to determine whether monetary-policy shocks affect economic growth. They used careful historical analysis to identify and focus on cases in which the policy stance changed for reasons not having to do with the current state of the economy.
经济史学家已经展示过这样做的方法。比如，笔者在伯克利大学的同事大卫和克里斯蒂娜夫妇在试图确定货币政策冲击是否会影响经济增长时就面临了类似的问题。他们使用了仔细的历史分析方法来辨认并集中关注那些出于与经济状况无关的因素而改变了政策立场的案例。这使他们得以分离出冲击对增长的影响。