Robert Hall of Stanford University and Nicholas Petrosky- Nadeau of the Federal Reserve Bank of San Francisco used the U.S. Census Bureau’s Survey of Income and Program Participation (SIPP) to divide households into four income levels, or quartiles. They found that in 2013, households in the lowest quartile earned 62 percent of their income from working, while households in the highest quartile earned 96 percent of their income from working. What might explain the difference in the percentage of income earned by working between these two groups? Is your answer relevant to determining the effects of government policy on reducing income inequality? Briefly explain.