The study looked at how people's income changes affect their spending habits. By analyzing income and spending data, researchers found a way to separate long-term income changes from short-term ones. They used a method called Monte Carlo simulation to test their approach and found it to be reliable. They also found that people tend to save some money to protect themselves from big, long-term income changes. By including information about how much money people typically save, the researchers were able to improve the accuracy of their method.