The 2020 elections are still 16 months away and yet pollsters are out in force, giving us just enough information to break out our crystal balls and make wildly irresponsible predictions. This is the last post in a four-part series looking at the Generic Ballot and its utility as an election predictor. You can read the first post in the series here.
The Republican Party’s structural electoral advantage in federal elections is well documented in liberal circles. Republicans won two of the last five presidential elections while losing the popular vote. The Senate — where states get equal representation — gives rural, Republican-leaning states undue voting power relative to their populations. Republicans have so heavily gerrymandered the House that Democrats are consistently underrepresented relative to their portion of the popular vote.
Our focus here at ESY is the House — questions about the presidency and Senate will have to wait. We’ll concentrate on the last claim: Do Democrats face a structural disadvantage in House elections? To start, it’s important to understand two measures of bias in the House. We’ll then look at how these biases have come into play historically and, finally, how that relates to the generic ballot.
The Median House District
One way to measure bias in the House of Representatives is to compare the median House district’s electoral margin to the national popular vote. If you were to line up all the House districts from most Democratic to most Republican, the median House district would be the one directly in the middle. Number 218 out of 435. The district that would tip control of the House from one party to the other. The distance between this district’s margin and the national popular vote is one way to measure the House’s bias.
In 2018, Democrats led the House Popular Vote by 8.6%. In the median House district, California’s 10th, Democrat David Harder won by 4.5%. If the whole nation voted 4.5% more Republican, Democrats would still have carried the popular vote by 4.1%, but lost CA-10 and, with it, control of the House. In this way, Republicans had a 4.1% structural advantage in the House in 2018.
David Wasserman of the Cook Political Report uses this measure to argue that Democrats have faced a disadvantage in the House since the 1960s.
The Seat Bonus
The other way to measure bias in the House bias is to measure each party’s “seat bonus”. A party’s seat bonus is the gap between their share of seats in the House and their share of the popular vote.
In a perfectly proportional system, a party that wins 53% of the vote would receive exactly 53% of the seats. The House, though, is decided by 435 individual elections rather than proportional allocation, making a perfectly proportional distribution of seats unlikely. In 2018, Democrats won 53% of the popular vote and won 235 of the House’s 435 seats, which translates to 54%. The Democratic seat bonus, therefore, is 1%.
This is perhaps a more intuitive way to measure the House’s bias. It also paints a more complex picture of the parties’ structural advantages and disadvantages in this legislative body. Unlike the “Median House District” measure, the “Seat Bonus”, over the years, has swung back and forth between the parties.
Tracking the “Seat Bonus”
The following graph shows Democratic and Republican overrepresentation in the House, measured by their proportion of seats minus their percentage in the national House popular vote, from 19721The 1972 redistricting was the first to take place under the Supreme Court’s “one person one vote” ruling which mandated districts of roughly equal proportion, making that election a natural starting point. to 2018. It’s a graph of each party’s “seat bonus”.2All data in the graph is rounded to the nearest 1%
The graph shows three eras in the House. From 1972-1992 Democrats consistently benefited from a seat bonus while Republicans faced a heavy seat penalty. From 1994 – 2008, things were a bit more muddled, with Republicans and Democrats both usually benefitting from a seat bonus, but Republicans typically getting more of a bump. Lastly, from 2012-2016 Republicans got a strong seat bonus while Democrats faced a penalty. The most recent election 2018, seems to break this last era of Republican overrepresentation, but we will have to wait to see where the trendline goes in 2020 and after.
These three eras line up almost perfectly with which party had control of the House. Democrats had majorities from 1972-1992, from 2006-2008, and again in 2018 while Republicans did from 1994-2004 and from 2010-2016. The party that won a majority in the House almost always received a bigger seat bonus. Out of 24 elections, only 1994 breaks the trend. And over these 24 elections, the party that won the House majority received an average 6% seat bonus. This bonus, however, has decreased from an average of 8% between 1972-1982 to 4% from 2008-2018.
The reason for the seat bonus deserves its own blog post and will be the focus next week. Some preliminary explanations:
1) Swingy seats are (proportionally) overrepresented. In 2018, there were 91 seats that fell in the range of +10 Republican to +10 Democratic. Since seats can range from +100R to +100D — a total range of 200 points — the 20-point range of +10R to +10D represents 10% of the total possible range. One might expect 10% of House seats to fall within this range. Instead, 91 seats (21% of all House districts) fell in this range. Because these close seats are overrepresented, a party will be disproportionately rewarded for marginal gains around 50% of the two-party vote.
2) Seats have different levels of elasticity — meaning they respond differently to changes in the national environment. According to FiveThirtyEight, for every change in 1% of the national popular vote, Michigan’s 5th District — the most elastic district in the nation — will move 1.24%. On the other side is Pennsylvania’s 3rd, which will only change .72%. Perhaps the swingy seats are also the most elastic, meaning that a party will be disproportionately rewarded for marginal gains around 50% of the two-party vote.
Again, these are just ideas. Next week we’ll dig into the data.
Below is chart similar to the one above, but this one uses the two-party popular vote, which excludes any votes for third parties.
It looks almost identical to the first graph, with one big exception. In this graph, both party’s trendlines are consistently a few percentages lower. When third party votes are included in the popular vote total, both Democrats and Republicans over-perform in House to a greater extent than when these votes are excluded. The reason for this is clear: third party votes rarely translate to real representation in the House. Third party votes increase the raw number of votes in the popular vote, meaning that Democrats and Republicans will receive a lower percentage of the total vote percentage. But because third party candidates almost never get elected, Democrats and Republicans do not see their overall representation in the House go down.
Tracking the Median House District
The Median House District measurement has shown a consistent bias in favor of Republicans for decades. Take a look at this graph charting the median seat in the House and Senate relative to the presidential popular vote. Every presidential year from 1968-2016 (excluding 1980), Republicans have had a two to six-point advantage. And that advantage has risen since the turn of the century, reaching about 5.5% in 2016.
This discrepancy comes from how Republican and Democrats are distributed among districts. Democrats are heavily concentrated in cities and urban areas; Republicans tend to be more spread out among rural, exurban and suburban districts. There are more districts with very high portions of Democratic voters than there are districts with very high portions of Republican voters. While party density makes it very easy for the individual seats, it also leads to a lot of wasted votes. Read my last post for more detail, but due to natural sorting and gerrymandering, Democrats waste more votes than Republicans. These wasted votes largely explain why the median House district is more Republican than the national popular vote. In 2018, Democrats won 180 seats by a 15% margin or greater while that number was just 126 for Republicans.
But…the Generic Ballot?
The Generic Ballot estimates the House popular vote which is used to project seat allocation between the parties. To understand the Generic Ballot’s utility at projecting seat allocation, it’s necessary to understand how well it predicts the House popular vote (which we covered in the first two pieces in this series) and how well that popular vote translates to seat allocation (which we covered in the last post and here).
According to FiveThirtyEight’s poll aggregator, Democrats lead the 2020 two-party Generic Ballot 53.7% to 46.3%, a 7.4% margin (as of July 13). This number is bound to change over the next year and a half. As 2020 approaches it will likely mirror the presidential election polls and in the meantime will track President Trump’s approval rating.
A 7.4% lead, though, would probably push Democrat’s past the Republican “Median House District” bias, giving them control of the House. Along with control of the House, Democrats would probably benefit from the “Seat Bonus” bias, giving them a greater than 53.7% (234 seats) share of House seats. Democrats didn’t get that “Seat Bonus” in 2018, winning about 8.6% in both the Popular Vote and seat allocation. However, as we saw from Republicans in 1994 and Democrats in 2006, it is common for a party to not receive a big bonus the first year that they re-take the House but then to see the bonus factor in the next election.
As we learned in the first post of this series, the Generic Ballot is pretty good measure of the national popular vote. It’s a good indicator of the national mood and predicts well how many House seats each party will win. We will end with two caveats to this. One: The Generic Ballot is much less reliable this far out from election day. Two: The House of Representatives is not decided by the national popular vote. It’s decided by 435 individual single-member districts with local factors and unique candidates. In this sense, there’s nothing at all general about House elections.