Does it matter that the wealthy turnout to vote at a rate of almost 99% while those making below $10,000 vote at a rate of 49%? It sure seems like it would, but for a long time many political scientists and journalists believed it didn't. In their seminal 1980 study on the question (using data from 1972) Raymond Wolfinger and Steven Rosenstone argued that, "voters are virtually a carbon copy of the citizen population." In a 1999 study, Wolfinger and Benjamin Highton find a slightly larger gap between voters and nonvoters, but still conclude, "non-voters appear well represented by those who vote."
This argument has been largely assimilated by pundits and also non-voters, 59% of whom believe "nothing ever gets done," and 41% of whom say "my vote doesn't make a difference anyway."
But more recent research suggests that the logic of wealth voters is sound — and that if the poor and middle class turned out at a higher rate, policy would shift leftward on economic policy. The most important study on the question is by Jan Leighley and Jonathan Nagler. They revisit the Wolfinger/Rosenstone thesis and find that, in fact, non-voters are not, "a carbon copy" of the voting electorate as previously assumed. They find that, "notable demographic, economic, and political changes that have occurred in the U.S. since Wolfinger and Rosenstone's classic statement [their 1980 book, "Who Votes"]." The most important difference that Leighley and Nagler find is that:
After 1972, voters and non-voters differ significantly on most issues relating to the role of government in redistributive policies. In addition to these differences being evident in nearly every election since 1972, we also note that the nature of the electoral bias is clear as well: voters are substantially more conservative than non-voters on class-based issues.
That is, after the New Deal consensus eroded, policy views became more polarized along class lines and the class-skewed nature of the electorate began to matter considerably. Non-voters skew left on a variety of issues:
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A Public Policy Institute of California (PPIC) study of Californians from 2006 finds that non-voters are more likely to support higher taxes and more services. They are also more likely to oppose Proposition 13 (a constitutional amendment which limits property taxes) and to support affordable housing (a more recent study finds similarly). More recently, a 2012 Pew study that examined likely voters and non-voters finds a strong partisan difference. While likely voters in the 2012 presidential election split 47% in favor of Obama and 47% in favor of Romney, 59% of non-voters supported Obama and only 24% supported Romney. The study also found divergence on other key policy issues, including healthcare, progressive taxation and the role of government in society.