Wristbands for voters are seen at a polling station during early voting in Chicago. (Reuters)

In November 2013, voters in Takoma Park, Md., made history. The city became the first place in the United States to grant 16- and 17-year-olds the right to vote in local elections. Since then at least one other community — neighboring Hyattsville, another suburb of Washington, D.C. — has followed that example. Activists have been campaigning for that right in communities across the country, from Memphis to Fresno, Calif. Fifteen states now allow 17-year-olds to vote in primaries for elections that will be held after they turn 18.

There are two good reasons to reduce the voting age. First, it is likely to help young people establish the habit of voting lifelong. Second, as my recently published research shows, it makes their parents more likely to vote as well.

Younger voters could use more years in which to develop the habit of voting. And parents could use the impetus to set a good example.

Why? Advocates argue that lowering the turnout age will boost political participation, both immediately and lifelong. Research shows that turnout is habitual: Those who come of voting age just before an election are more likely to vote in subsequent elections. In the years just after becoming voters, however, young voters’ turnout drops precipitously for several years; and young people who move out of their parents’ homes are also often likely to stop voting for several years. In other words, if more young people started the habit of voting while 16 or 17 and still living at home, they might be more likely to establish a habit of voting lifelong.

But there’s another reason to reduce the voting age, according to my recent research: When young people vote, their parents are more likely to vote, too. Examining detailed, administrative data from Denmark, I found a “trickle up” effect, in which parents vote because of their children — both to set the example and to keep up with their civic habits.

Here’s how I did my research

Denmark has some of the world’s most detailed administrative records of its population (which makes it a paradise for social scientists). Every permanent resident of Denmark has a civil registration number, which is linked to, among many other things, one’s complete residential history and one’s parents’ civil registration number. My research team also linked the civil registration number to the official voter lists, which showed whether a person had voted.

Denmark has no voter registration requirements; any citizen, and some noncitizens in local and European elections, can vote, beginning at age 18. Imagine a voter turning 18 on election day. Some days before the election, she will automatically receive a polling card telling her when and where to vote; on election day she may go vote. Another person may turn 18 the day after the election. She will not receive a polling card and will not be welcome in the voting booth — even though only one day of life separates the two who are, in all other respects, peers.

Now take the parents of these two. The parents of the 18-year-old will have a child who can vote; the parents of the 17-year-364-days-old will not. Both pairs of parents may want to instill civic virtues in their child.

But only in the household with the young potential voter can the parents and the young voter go to the polls together. So are parents of newly enfranchised voters more likely to vote in elections, modeling good civic behavior, than parents of not-quite-enfranchised voters?

Any two pairs of parents are obviously different on a wide range a factors that influence voting, not just having a voting-age child or not. But for this research I was able to look at large groups of parents of eligible and ineligible teenagers, in which all the differences cancel out — except for whether their children are old enough to vote. I compared the turnout rates of parents whose children are barely old enough to vote to those of parents whose children are not old enough to vote by the same bare amount. I used an algorithm to pick an optimal window for each election, which means that the estimation windows varied from 38 to 56 days. As an alternative, I also compared turnout rates within windows of just one day, two days, three days, a week and a month.

Across four elections in Denmark, on average, when their children came of voting age right around the election turnout increased 2.7 percentage points for the parents.

But that was only true for parents who lived with their children. Parents with voting-age children at home are about 4 percent more likely to vote; parents whose voting-age children do not live with them are unaffected.

Many children start leaving home around age 18 — meaning that many young people will leave home before the first election in which they can vote. If the voting age was 16 or 17, more children would still live with their parents in their first election — and both groups would be a bit more likely to vote.

A handful of countries already have voting ages lower than 18

Several countries have had at least some experiences with lowering the voting age. Austria has for about a decade allowed 16-year-olds to vote in most countrywide elections. Scotland allowed 16-year-olds to vote in the 2014 independence referendum and has since extended this to elections for the Scottish Parliament. Since 1988, Brazil has allowed 16-year-olds to vote in all elections, including presidential elections; from age 18 on, voting is compulsory.

But can younger teenagers vote responsibly?

The main concern with lowering the voting age is whether 17- or even 16-year-olds are old enough to vote responsibly. Opponents argue that they are not; proponents argue that they are. Research from the Austrian and Scottish experiences suggest that 16- and 17-year-olds are as engaged and interested in politics and make voting decisions as well as older voters. Research from Norway, on the other hand, concludes that young voters are less mature in how they make those decisions.

Jens Olav Dahlgaard is an assistant professor in political science at the Copenhagen Business School.