The gap between rhetoric about income inequality and action to deal with it is sizable. There are many reasons for that, but one possible explanation, according to a provocative new book, is the contrasting views of Americans who vote and those who do not.

The book is titled “Who Votes Now? Demographics, Issues, Inequality, and Turnout in the United States.” The authors are two political scientists, Jan E. Leighley of American University and Jonathan Nagler of New York University.

“Who Votes Now?” is a thoroughgoing examination of voter turnout patterns from 1972 through 2008 and offers much to chew on. But its most important finding, the authors say, is that, on crucial questions about economic policy and redistribution, those who vote do not represent the views of those who do not vote.

“Voters are significantly more conservative than nonvoters on redistributive issues and have been in every election since 1972,” they write. “Voters may be more liberal than nonvoters on social issues, but on redistributive issues, they are not. These redistributive issues define a fundamental relationship between citizens and the state . . . and are central to ongoing conflicts about the scope of government. It is on these issues that voters offer a biased voice of the preferences of the electorate.”

The book is a reexamination of ground covered three decades ago in a foundational study of American political behavior titled “Who Votes?,” by Raymond E. Wolfinger and Steven J. Rosenstone. That work concluded, among other findings, that there were no significant differences between voters and nonvoters.

The issue of income inequality is now drawing the attention of elected officials in ways it did not just a few years ago. New York Mayor Bill de Blasio won a huge victory in November after making clear that he intended to attack the problem in his city. President Obama, in a speech last month, pledged anew to devote more of his remaining time in office to finding ways to narrow the gap between rich and poor.

But what is to be done? De Blasio offered clear choices in New York, but his electorate is hardly representative of the nation as a whole, and his remedies are yet to be tested. Whether other politicians are ready to emulate him is one of the questions that will frame the coming election year and probably the 2016 presidential race. The progressive wing of the Democratic Party is stirring, but it’s not clear how widespread its influence will be.

One question Leighley and Nagler address is why there hasn’t been more attention to, and action on, the issue of income inequality by politicians at a time when the problem has grown steadily worse. To answer it, they looked at different aspects of the question of who votes and who doesn’t and whether the balance has changed.

The authors found that there have been some important demographic changes in voting patterns within the overall electorate. Women are now more likely to vote than men. And the gap between black and white participation has narrowed significantly. In the most recent election, blacks voted at higher rates than whites in some states.

But in other ways, the overall shape of the electorate has been stable since 1972. During a time of rising income inequality, wealthier and better-educated people continue to vote “at substantially higher rates” than poorer, less-educated people. That gap existed 40 years ago and still does.

Politicians and others have looked for ways to make it easier to vote. New laws that allow people to register on Election Day are one example. Those changes have had a positive, if modest, impact on the percent of eligible voters who actually cast ballots, the authors conclude, enough to change the outcome in a close election.

But they haven’t changed the imbalance in participation rates among wealthier vs. poorer Americans, nor have they affected the degree to which politicians have sought to address income inequality. The problem has gotten worse as voter participation rates have increased.

Another conclusion is that eligible voters are more likely to cast ballots if they see a difference among the candidates. “If citizens see no differences in what candidates are offering, then, there really is very little reason to show up at the polls,” according to the authors.

That finding itself is not all that surprising. What is striking is that income and education levels appear to influence whether people see substantial differences between candidates.

Those at the higher levels of the income scale — in other words, those who are more likely to vote — are likelier to perceive ideological differences between candidates. Those at the bottom of the scale, however, see few differences between the candidates. As the authors put it, “The poor cannot respond to policy choices they do not see.”

Why don’t nonvoters see more differences between candidates? Many nonvoters pay less attention to campaigns and therefore know less about those running. Residents of non-battleground states rarely see candidates and are not exposed to candidate advertising. Campaigns spend more time and money targeting known voters, rather than those who generally do not vote.

As recent elections have shown, those who vote are polarized ideologically, but as the authors note, they are as a group more conservative than nonvoters on issues of redistribution. “To the extent that elected officials respond to voters,” they add, “we expect that public policies regarding redistribution and inequality will be less generous than they would in the case of universal turnout.”

There are some questions that Leighley and Nagler cannot answer. One is how much election outcomes really would change if there were something approaching universal turnout. Do voters really cast ballots on the basis of perceived policy choices, or according to party labels or candidates’ personal attributes? Would candidates offer a broader range of policy proposals if they believed they could capture more of the nonvoters?

Still, “Who Votes Now?” provides a fresh and valuable look at questions basic to the functioning of a democratic society. As the authors put it, under the current makeup of the electorate, “democratic equality is doubtful.” That observation alone could prompt some politicians to think about the issue differently.