It's often hard to evaluate how election turnout changes from one place to the next over time because no two elections are the same. Populations rise and fall; candidates and races capture the public's attention or don't; the people running the process do a good job or they totally botch it. It's why it can be hard to evaluate the role of voter ID laws in changes in turnout: Did it drop because of the new law or did it drop because no one cared about the governor's race? (A Government Accountability Office report in 2014, by the way, controlled for a variety of factors to determine that it was the new laws -- at least in some cases.)

Before the New York primary on Tuesday, WNYC reported that more than 120,000 people were dropped off the voter rolls in Brooklyn. Some people had moved, some had been labeled as "inactive" -- but the scale of the change prompted a lot of concern. Mayor Bill de Blasio (D) released a statement pledging to address voting issues that were reported on Tuesday. The board of Elections suspended the chief clerk at its Brooklyn office while they investigated what had happened.

I was curious how much that purge may have affected the results in the city on Tuesday. So I pulled some numbers.

How best to see if Brooklyn's turnout changed? Well, we can compare it to the other boroughs. After all, all five voted in the Democratic primary on Tuesday, just as all five did in 2000, 2004 and 2008. We can see how much of that total turnout came from Brooklyn and how much came from the other boroughs.

As it turns out, Brooklyn was a higher percentage of the voting than any of the other four on Tuesday -- and grew as a percentage of that turnout since the last contested Democratic primary eight years ago.


(The numbers we use here come from U.S. Election Atlas. Below, we use data from the state board of elections.)

But there may be other factors at play. Brooklyn is a popular place to live, after all. Maybe there was also a surge in population. Maybe there were differences in voter registration.

Take Staten Island. The city's smallest borough is also its most Republican, so it is a much smaller percentage of the Democratic primary electorate than it is a percentage of the city's population. It's a slightly higher percentage of general election turnout, because Republicans tend to vote more. As do wealthier people, and Staten Island has the highest median household income of any of the boroughs.


Close behind is Manhattan. Manhattanites vote more heavily than other boroughs, too, outperforming their percentage of the city itself. In 2004, a highly disproportionate number of people in Manhattan voted in the (unimportant) Democratic primary.


But let's get back to Brooklyn.


The percentage of the city that lives in the borough and the percentage of New York City Democrats who are registered there has been pretty constant. But in the 2016 primary, for the first time, the borough outperformed its population. It's 30.8 percent of New York; it was 31.4 percent of the Democratic electorate.

This isn't enough to tell us that turnout wouldn't have been higher still without the weirdness. It's not enough to tell us that there wasn't any problem at all. But the numbers also do not suggest that turnout in Brooklyn suffered greatly thanks to that purge of voters -- something that might help assuage any concerns that the results of the primary were affected.