The study looked at how public and private debt affect economic growth. They found that when total debt reaches 220% of GDP, the interaction between public and private debt has a negative impact on growth. This means that the combined effect of public and private debt is greater than just the sum of their individual effects. The study also showed that the interaction between public and private debt is likely influenced by household debt and public debt. The findings suggest that the true impact of debt on growth is underestimated if we only look at individual debt levels without considering their interaction.