Do single member districts hurt Democrats?

Even without a partisan gerrymander, Democrats cannot win a full 30% of seats unless Democratic voters are clustered in an optimal way.

In 2010, Democrats won only 17 of the 75 seats in the Utah House of Representatives. That’s 23% of the seats. But if you add up all the votes cast statewide, you’ll find that 30% of votes in these 75 races were cast for Democrats. How is it that Democrats can win 30% of votes but only 23% of seats? Some Democrats have cited this sort of disparity as evidence that the districts were gerrymandered back when they were drawn in 2001.

As it happens, they are jumping to conclusions. In Utah, we use single-member districts (SMDs), where the winner in each district is the one candidate who wins the most votes. There are many, many, many other electoral systems used around the world, and each is just as democratically valid as SMDs. Each has its benefits and drawbacks. The major drawback of SMDs is that they tend to magnify partisan disparities. Even with perfectly fair districts, we would expect our SMDs to award more seats to Republicans than their vote share might suggest.

A not-so-hypothetical thought experiment

To see how this is true, imagine that Utah voters were exactly 70% Republican and 30% Democratic. (That shouldn’t be too hard to imagine.)

If Republicans and Democrats were evenly sprinkled throughout the state, and if the 75 districts were randomly drawn, then you would expect every district to be (on average) 70% Republican and 30% Democratic. And what happens if every district is 70% Republican? Republicans win 100% of the elections. In other words, even without any sort of partisan gerrymander, you would expect a 70% Republican voting majority to produce a 100% Republican legislative majority.

Now, let’s consider the opposite example. Instead of being evenly sprinkled around the state, suppose that Democrats and Republicans were concentrated into completely separate areas, so that 30% of districts are 100% Democratic and 70% of districts are 100% Republican. Democrats would win 30% of votes statewide and also 30% of seats.

Obviously, Democrats and Republicans are not evenly sprinkled around the state, nor are they clustered into ghettoized districts. In some areas, such as Salt Lake City, Park City, and Moab, Democrats are clustered enough together that they form a local majority. Because of this clustering, we would expect Democrats to win seats in those areas. But we still would not expect them to win 30% of seats statewide. After all, many Democratic votes are “wasted” in Utah County and other overwhelmingly Republican areas. Even without a partisan gerrymander, Democrats cannot win a full 30% of seats unless Democratic voters are clustered in an optimal way.

Yes, single member districts hurt the minority party

So, do single member districts hurt Democrats? Without question. Single member districts create a disparity that over-represents the majority party. Multimember districts might be better, or they might even be worse–depending on the details of how they are set up. But that’s not the point of this post, so I’ll hold off for now.

We see that the presence of SMDs might be enough to explain why Democrats win 30% of the legislative votes statewide but only 23% of the seats. Note the word “might.” It’s also possible that SMDs cause only part of that disparity, with partisan gerrymandering causing the rest. I’ll address that in my next post.

This is part of a series of posts about redistricting in Utah. For an overview, read the introductory post. My talented research assistant, Robert Richards, contributed heavily to this series.

Possibly related posts:

About Adam Brown

Adam Brown is an assistant professor of political science at Brigham Young University and a research fellow with the Center for the Study of Elections and Democracy. You can learn more about him at his website.
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