The disenfranchisement of felons has been a hotly debated subject recently, in part because such states as Florida and Louisiana have made it easier for people with criminal convictions to vote after they finish their sentences.

Felon disenfranchisement remains important. But the effects of the criminal justice system on voting patterns go well beyond laws that literally strip people of their voting rights. According to research I recently conducted, even a misdemeanor charge leading to a short jail sentence — often of only a few days or weeks — can lead to a significant decrease in the likelihood of future voting. The effects are heavily concentrated among black voters.

Given that millions of Americans are jailed for misdemeanor offenses each year, the subsequent effects on voting behavior could be significant: Extrapolating from the numbers I found in one Texas county, roughly 100,000 to 150,000 black voters nationwide could be staying home in a given presidential election, as the result of a short stint behind bars.

The study focused on Harris County, Tex., which includes Houston, the state’s largest city. I tracked the cases of over 100,000 people charged with misdemeanors, which include offenses ranging from drug possession to theft to simple assaults, between 2008 and 2012. They faced jail sentences of up to a year but no loss of their voting rights. I then looked at whether these people voted in the 2012 presidential election. Overall, people who went to jail were a few percentage points less likely to vote than those who did not serve time. But among African Americans in the study, the effect was profound: Those who went to jail were a full 13 percentage points less likely to turn out. In Harris County alone, that level of voting decline adds up to several thousand lost votes, enough to potentially swing some local elections.

Researchers, not to mention people who have spent time in jail or know someone who has, already know quite a bit about the harsh effects that even short jail sentences have on people. They cause job losses and other economic hardships, prompt evictions from houses and apartments, and place intense stress on family relationships, leading to divorce and other ruptures. Experiences like arrest or incarceration also affect how people view the government. The social scientists Amy Lerman and Vesla Weaver, for instance, have shown that people who have been arrested or incarcerated tend to believe that they would always be viewed by their government as criminals, not full citizens.

So it was plausible jail time could make people less likely to vote — either by changing their attitudes or by making their life sufficiently difficult that they just couldn’t make it to the polls.

But it was a hard proposition to test, for all sorts of reasons. In the population at large, people who are charged with misdemeanors and sentenced to jail, are different from those who don’t in many ways; they’re often younger, poorer and less likely to trust government to begin with. So we might look at their voting habits and conclude that we were identifying a “jail effect” but really just spotting those other differences.

To get around that problem, I made use of a technique that other researchers have used to study the effects of incarceration: In some courthouses, cases are randomly assigned to different courtrooms, which vary consistently in the severity of the sentences they mete out. (Judges are the main thing distinguishing these courtrooms, but other personnel also vary, and they could also influence outcomes.)

This means that otherwise similar people, facing similar charges and with similar backgrounds, are more or less likely to be sent to jail simply because of how they fared in the courtroom assignment lottery. Harris’s misdemeanor court system uses this kind of random assignment; it assigned cases among 15 courtrooms at the time of my study. Tracing people facing similar charges but different courtroom assignments (and thus different risks of being sent to jail) made appropriate comparisons possible. I then used public voting records to find out whether people turned out in the next presidential election after their arrest (2012), as well as their voting history in the past.

The racial discrepancy in the findings was striking: White people sent to jail voted a bit less often, but black people turned dramatically away from voting. Jail time reduced their voting participation rates from roughly 26 percent to 13 percent. (And this wasn’t because people were still behind bars on Election Day — these were all post-release effects.)

What explains the racial disparity? Racial differences in people’s risk of getting arrested and charged with misdemeanors is probably one factor. Think about it this way: If black neighborhoods and residents face more scrutiny from police, or lower standards of evidence for charging them with misdemeanor crimes — and evidence suggests both observations are true — then we might expect that the legal system would cut a wide swath through black communities, pulling in all sorts of people, including those who vote regularly.

White people charged with misdemeanors, on the other hand, might live less stable lives and be less likely to vote to begin with, and so be less likely to change their behavior after incarceration. Indeed, when I looked at the data, that turned out to be the case. Examining pre-arrest voting patterns, I found that the black people in the sample had previously voted at much higher rates than their white counterparts. That means there was a lot more room for them to stop voting after being incarcerated, either because they were too busy dealing with life crises, or because they grew to feel more strongly that the government didn’t care what they had to say.

There is a growing body of evidence suggesting that jail time may not be an effective or cost-efficient way of reducing crime, and that it carries many collateral consequences — job loss, housing instability, health problems and more — for the people jailed, as well as for their families and communities. My work suggests that we should also worry about jail’s political consequences, even in the case of short jail terms. The legal system disproportionately pushes black voters out of the electorate, and the problem goes far beyond felon disenfranchisement.