The study looked at how changes in the U.S. monetary policy affect different types of financial institutions' balance sheets. They found that when interest rates go up, banks and other financial companies reduce their assets, while money market funds increase their assets. These balance sheet changes are just as important as changes in interest rates in affecting the economy. However, before the financial crisis, these effects were not as significant. To prevent future crises, it may be necessary to use other policies alongside interest rate changes.