The study looked at how changes in income tax and payroll tax rates in France affected people's gross labor income. They found that when income tax rates went up, people's labor income decreased slightly, but when payroll tax rates changed, there was no effect on labor income. The average tax rate didn't have much impact on income tax, but it had a big impact on payroll tax. This could be because people changed how much they worked in response to income tax changes, especially married women. Overall, the findings suggest that income tax changes affect labor supply, while payroll tax changes affect how much people actually earn.