‘Fair’ Districts in the US House, or the lack thereof

This is a quick1 little demonstration I made for my POLS 206 class to demonstrate how single member districts in the House of Representatives can cause weird stuff to happen. The map shows the composition of the House delegation from each state. House delegations from red states are mostly Republican, those from blue states are mostly Democratic, and those from purple states are split in some way.

What I want to demonstrate to my class is the difference between the composition of a state’s House delegation and the popular vote for members of the House in that state. In Maine, for example, two out of two Representatives are Democrats, but 38% of the state’s voters voted for a Republican representative. If you believe that a ‘fair’ House delegation is one in which the number of Rs and Ds reflect the split between Rs and Ds in the state’s voters, then Maine should have 1 Republican rep and 1 Democratic rep (0.38*2=0.76, rounds to 1 Republican). When you mouse over a state, the state will change color to reflect the House delegation split that would most accurately mirror the popular vote split. Both these numbers are shown in the upper right corner of the map.

Partisan Composition of State House Delegations

Some states don’t change at all. Wyoming has a single Republican representative and this is as it should be! Only 26% of the electorate in 2012 voted for a Democratic representative, and it doesn’t make much sense to say that a fair split is for Wyoming to have 0.74 of a Republican and 0.26 of a Democrat. A fair split for Wyoming is 1 Republican and 0 Democrats. Look at Pennsylvania though. Pennsylvania has 18 seats, and the current split is 5 Democrats and 13 Republicans. Democrats received 51% of the popular vote for House representatives, so it seems like a fair split would be for Democrats to get 0.51*5 rounded off, which would be 9 seats! That’s a huge difference!

Are these discrepancies attributable to gerrymandering of some sort? Maybe, but it depends on what you consider gerrymandering. Consider the fake state below that has a population of 25: 15 Republicans and 10 Democrats.2

R R R R R
R R R R R
R R R R R
D D D D D
D D D D D

Let’s say this state receives 5 seats in the House. There are a couple of different ways we could district this state to produce starkly different results. First, we could create five Republican seats, each with a 3-2 Republican voter advantage:

R R R R R
R R R R R
R R R R R
D D D D D
D D D D D

We could draw horizontal lines to create 3 very safe Republican districts and 2 very safe Democratic districts:

R R R R R
R R R R R
R R R R R
D D D D D
D D D D D

We could also draw lines to create 3 Democratic districts and 2 Republican districts:

R R R R R
R R R R R
R R R R R
D D D D D
D D D D D

Which of these maps feature gerrymandering and which do not? You have to draw districts of some sort, and there is no obvious ‘natural’ way to draw them. A bunch of horizontal districts seems about the same to me as a bunch of vertical districts, but horizontal districts in this state produce a 3-2 delegation while vertical districts produce a 5-0 delegation! By one criterion, the second map is fair, because the House delegation split will be identical to the voter split (3:2 proportion of R:D in both cases). But there are other ways we could define a fair map! So the fact that House delegations don’t always reflect the partisan makeup of state voters isn’t necessarily due to gerrymandering. It’s just a natural consequence of having single-member districts.

For further evidence of this, take a look at California on the map. California has a bipartisan citizens redistricting commission. A supermajority of Democrats and Republicans on the commission have to sign off on the districting plan for it to become law. This should create a relatively fair map, but as you can see from mousing over California, Democrats are actually over represented by about 10%.

  1. It should have taken like an hour but CSS.
  2. This whole example was first shown to me by Michael Crespin so thanks Mike.
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