The tax system in Norway became less fair in the 1990s, even though the way taxes were distributed stayed the same. This happened because high-income earners had to pay less in taxes, especially after a big tax change in 1992. This made the gap between rich and poor people bigger. The researchers looked at individual income data to see how these tax changes affected income inequality. They found that the tax changes made it easier for rich people to keep more of their money, which made income inequality worse.