Allowing felons to vote could change American politics
voting us election
voting us election

(A voter filling out a ballot for last year's US presidential primary election in a voting booth in Stark, New Hampshire.Mike Segar/Reuters)

An estimated 6.1 million American adults were not allowed to vote in the 2016 election because they had a felony conviction on their record.

Most had already served their sentences and returned to their communities. The majority of US states take away felons' voting rights, occasionally for life.

This disenfranchisement affects an estimated one in 40 adult Americans, or 2.5% of the total US voting-age population, according to The Sentencing Project, a group that advocates criminal-justice reform.

That number is greater than the entire population of Missouri, and it's the largest single group of American citizens who are barred by law from participating in elections.

So many people are barred from the polls that some worry their absence could change election results. One study even suggested that allowing felons to vote in Florida could have tipped the 2000 presidential election to Democrat Al Gore.

About half of US states have loosened restrictions in recent years. But how this might affect the country's fractured politics is more complicated. Would ex-felons turn out to vote? And if they would, can we predict who'd benefit?

The US is a huge outlier when it comes to incarceration

The US has the highest incarceration rate in the world, with about 670 inmates per 100,000 residents, according to figures from the International Center for Prison Studies. Some estimates put the figure higher.

That rate is about five times the average of other developed economies in the Organization for Economic Cooperation and Development. The next-closest OECD state is Israel, which has an incarceration rate of about 250 inmates per 100,000.

Incarceration Rate by OECD Country
Incarceration Rate by OECD Country

(Skye Gould/Business Insider)

The number of Americans incarcerated has increased over the past 25 years.

The rate for US residents ages 18 and up rose from about 310 per 100,000 in 1980 to about 870 per 100,000 in 2015, a spike correlated with the "war on drugs"-era tough-on-crime policies. The rate peaked in the mid-2000s at about 1,000 per 100,000.

Incarceration Rates 1980–2015
Incarceration Rates 1980–2015

(Skye Gould/Business Insider)

Which brings us to the first divide: the disenfranchisement of those with a conviction

Few major economies around the world allow inmates to vote. Politicians and voters generally argue that if a person does not follow the law, then that person should not get to choose lawmakers.

In the US, the Fourteenth Amendment grants states the authority to deny voting rights to those with criminal convictions, and then states can come up with their own rules for restoring those voting rights if they choose.