A basic analysis of the 2018 US midterm elections suggests it was less gerrymandered than other recent elections for the House of representatives
Now that the ballots for the 2018 House of representatives election have been counted, how badly was the vote gerrymandered?
Gerrymandering is the creating of political districts to maximize the number of representatives a political grouping gets per vote.
The degree of gerrymandering can be approximated by calculating the difference between the outcome of a proportional voting system and the actual districted representatives each party gains.
Here's a look at the last 5 elections to the House of representatives.
In this congress, the Democrats have 235 representatives, the Republicans have 199 and there's 1 other representative.
Voter turnout was 50,3%, the highest for a midterm election since 1914.
The Democrats got 53,5% of the popular vote and 54,0% of the seats. The Republicans got 44,8% of the vote and 46,0% of the seats. Others got 1,8% of the vote and a single seat.
Since the Republicans are no longer getting vastly outsized representation, is gerrymandering dead?
If the US would have had a proportional voting system, 7 of the 435 seats would have been distributed differently in 2018.
The Democrats would have had 3 fewer representatives, the Republicans would have had 4 fewer and others would have had those 7 seats.
Here are the similar figures for the last five elections.
| Year | Votes per seat ('000) | Dem diff. | Rep diff. | Other diff. |
|---|---|---|---|---|
| 2010 | 199 | -3 | +18 | -15 |
| 2012 | 281 | -11 | +27 | -16 |
| 2014 | 179 | -10 | +24 | -14 |
| 2016 | 295 | -15 | +27 | -12 |
| 2018 | 261 | +3 | +4 | -7 |
The change from getting 27 seats "wrong" in 2016 to 7 seats "wrong" this year is large and changes the historic trend.
Turns out that higher turnout led to more accurate representation in 2018. Who would have guessed.
(There are many other additional possible explanations for why this has changed too)
If we just look at the two major parties, what does this mean in real terms?
Here's an overview of the average difference in the number of voters the Democrats have needed for each seat they actually got in the last five elections compared to the Republicans.
| Year | Additional Dem voters for a seat |
|---|---|
| 2010 | 8,6% |
| 2012 | 19,4% |
| 2014 | 16,6% |
| 2016 | 21,4% |
| 2018 | 0,8% |
There are other ways of trying to engineer specific election results.
This basic overview only looks at people who actually vote. Therefore it obviously doesn't consider those who are prevented from voting in the election process, whether that's from voting requirements, accessibility of polling places, registration requirements, etc.
It will be interesting to see what happens in 2020.
Is this a trend that'll continue?
Is it just a blip because those gerrymandering haven't been able to predict what party voters vote for in today's political climate?
What about turnout?
I would say that your analysis suggests that voting turnout at the 2018 mid-term US elections outweighed the gerrymandering in place.
Gerrymandering is the practice of drawing electoral boundaries to favour one party or candidate over another. I believe that the electoral boundaries across the USA didn't change significantly between 2016 and 2018. Even I, here in Australia, would have seen something about such a widespread re-drawing of the electoral boundaries - especially because gerrymandering is such a big problem in the US electoral system. That sort of change would have made news.
No, gerrymandering itself didn't change.
What changed was that more people voted. In your analysis, you say the 2018 mid-term elections had the highest voter turnout since 1914.
Specifically, a lot of Democrats wanted to vote in this election. Your own statistics show that. Over the preceding 4 elections, an average of 46.8% of voters voted Democrat. This jumped to 53.4% in 2018. That's a significant jump - and I suspect it's enough of a jump to outweigh the inherent bias built into the electoral system by gerrymandering. Even in districts where the boundaries are drawn to favour Republicans, Democrats can win if enough of them come out to vote.
Gerrymandering didn't go away. It was just outweighed by more Democrats voting.
this. in fact, significant gerrymanders probably kept republicans from losing considerably more house seats than they would have under fairer lines in last year's elections. in particular, ohio's delegation remained 12R-4D despite republicans only winning 52% of the vote there, and in texas the delegation is 23R-13D despite republicans barely winning 50% of the vote there.
All data from the elections from each individual election result page.
Here's some more data for those interested in that.
First the proportion of votes for the various political groupings compared to the percentage of seats they got in each election.
*One seat
Here are the raw numbers of voters each political grouping required for each seat in the House of representatives they got in each election.
*Per set for the one seat