Demonstrators in Leimert Park in Los Angeles mourn the shooting death of Michael Brown at the hands of police in August 2014. (Michael Nelson/European Pressphoto Agency)

Black people in the United States continue to be sicker and die sooner than whites. These health inequalities have persisted even though they are contrary to what some policymakers anticipated in the post-civil rights era, when blacks gained greater access to health services, employment opportunities and other determinants of health. Because blacks lag behind whites in infant mortality, life expectancy and a wide variety of morbidity rates, they suffer from “excess mortality” — that is, black deaths that would not have occurred had the death rate among blacks been the same as that among whites.

But what are the political consequences of excess mortality among blacks? A new article by Javier Rodriguez, Arline Geronimus, John Bound and Danny Dorling — “Black lives matter: Differential mortality and the racial composition of the U.S. electorate, 1970-2004” — answers this question. It finds that excess mortality among blacks reduces their voting power significantly, perhaps costing Democratic candidates several elections.

Rodriguez and colleagues estimate that excess deaths among blacks totaled 2.7 million between 1970 and 2004, that 1.74 million would have been of voting age, and that 1 million would have voted in the 2004 election. Combining excess mortality with the consequences of felon disenfranchisement, they find that about 1 in 7 blacks (15 percent) did not have the opportunity to vote in 2004 for one of these two reasons.

In that election, 166 presidential electoral votes (62 percent of the 270 needed to win) were contested in states where at least 15 percent of voting-age blacks did not participate because of premature death or felony disenfranchisement. Nevertheless, even though the authors calculate that John Kerry would have won 86.6 percent of the black votes lost to excess mortality, these deaths were not enough to have changed the outcome of the presidential race.

But in down-ballot races, the story is different. The authors estimate that between 1970 and 2004, Democrats would have won seven Senate elections and 11 gubernatorial elections were it not for excess mortality among blacks.

All of these numbers could actually be underestimates. Given limitations in data availability, the authors could calculate excess mortality only over the 1970-2004 period and, thereby, could not count deaths that would have accrued among earlier cohorts.

The authors’ data also are not perfect in other respects. Their calculations of excess mortality could not take into account socioeconomic status, for example, because health records in the United States often do not contain information about income and education.

There is also the broader challenge of identifying a counterfactual — that is, what would have happened had these additional blacks been eligible to vote? Answering this question depends on assumptions, such as those necessary to estimate how these blacks would have voted. Of course, we cannot know how the strategies of parties or candidates would have changed had these additional black voters been in the electorate.

Nevertheless, the article demonstrates that black people are dying much sooner than whites, on average, and that this fact may affect the outcomes of elections. It is crucial to be clear about the first point to fully appreciate the second. Research has shown that blacks are not dying in excess because of differences in genetic endowment or health behavior. Instead, health disparities reflect racial and class inequality and an accumulation of stressors, including segregation, discrimination, exposure to pollution and unequal access to health-care resources, to name a few.

These social determinants of health depend to a great extent on politics. Thus, the harsher physical and social environment that blacks face is the direct and indirect result of political decisions, past and present.

Ultimately, the authors point out a troubling feedback effect whereby premature deaths among blacks affect the balance of political power among blacks and whites in the United States. And given the differences between blacks and whites in their political agendas and policy views, excess black death rates weaken overall support for policies — such as antipoverty programs, public education and job training — that affect the social status (and, therefore, health status) of blacks and many non-blacks, too.

The tragic deaths of unarmed black men have again generated conversations about racial inequality in the United States. This paper shows us another way in which “black lives matter” — one that affects a key element of our representative democracy: the composition of the electorate. For this reason, excess mortality of blacks relative to whites has consequences not only for the health of blacks but also for the health of our democracy.

Dean E. Robinson is associate professor of political science at the University of Massachusetts at Amherst.