The study looked at how people in middle-income countries react to changes in fuel prices and income over time. They analyzed data from 28 countries between 1990 and 2019. The results show that people in these countries are somewhat sensitive to changes in fuel prices and income. On average, when income goes up, people tend to use more fuel, but not by a huge amount. And when fuel prices go up, people tend to use a little less fuel. Overall, there is no strong evidence that people in middle-income countries are using less fuel because they are becoming more efficient or that they are less affected by changes in fuel prices.