The article "Optimal Mortgage Design" explores the best way to structure mortgages. The researchers analyzed different mortgage options to find the most efficient design. They discovered that mortgages with fixed interest rates are better for borrowers in the long run, even though they may seem more expensive at first. Adjustable-rate mortgages can be riskier because the interest rates can change unpredictably. Overall, the study suggests that fixed-rate mortgages are the optimal choice for most borrowers.