The article examines how changes in mortgage interest rates affect people's decisions to take out mortgages. By analyzing data on millions of mortgages, the researchers found that a 1% increase in interest rates leads to a 2-3% decrease in mortgage demand. They also discovered that some borrowers take out second mortgages instead of increasing their total mortgage debt. Overall, the study predicts that small increases in fees charged by certain mortgage companies would have minimal impact on new mortgage loans.