The study looked at how changing tax deductions in Japan could affect income inequality. They used a method called microsimulation with data from a survey. The results showed that changing deductions for spouses didn't do much to reduce income disparity. However, switching deductions to tax credits for individuals slightly decreased income inequality. To make a bigger impact, more deductions would need to be removed and tax credits introduced. Additionally, a new idea called "discount on social insurance premiums" could help reduce income inequality by using money from personal income tax.