The study looked at how rules about how much money banks need to have on hand affect how much they lend. By analyzing how banks make decisions about lending money when they have to follow these rules, the researchers found that the size of the extra money banks need to keep is the most important factor in how much they lend during economic ups and downs. Making banks keep more money on hand can make them lend less when the economy is doing well, and lend more when the economy is struggling.