From the Summary: "Although not itself a subject of legislation, the shape of the income distribution enters Congress's decision-making process concerning such policy issues as taxes, means-tested benefits, and social insurance programs. Congress also considers legislation specifically in the name of those in the middle class, which is variously defined as some income level or income range within the distribution of U.S. households with income. After briefly analyzing the distribution of household money income in 2010, the report attempts to put the term 'middle class' into some perspective. The first key point of the report is that, although there are a variety of ways to describe the income distribution, all show that income is concentrated among high-income households. [...] The second major point is that there is no official government definition of who belongs to the middle class, perhaps because the term means different things to different people. [...] Thirdly, it appears that both absolute and relative income may determine who belongs to the middle class. [...] The last key point of the report is that the middle class appears to identify itself relative to a reference group (e.g., the incomes of others in their neighborhood or in their companies)."
CRS Report for Congress, RS20811