Their first task is to put banks into the models. Today’s mainstream macro models contain a small number of “representative agents”, such as a household, a non-financial business and the government, but no banks. They were omitted because macroeconomists thought of them as a simple “veil” between savers and borrowers, rather than profit-seeking firms that make loans opportunistically and may themselves affect the economy.
This perspective has changed, to put it mildly. Hyun Song Shin of Princeton University has shown that banks’ internal risk models make them take more and more risk as asset prices rise, for instance.