Tag Archives: House elections

Vote Surge and Decline

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Hmmmm. I wonder what this is about? (OK: tl;dr it is about midterm elections and what to expect in 2022).

“Surge and decline” is the title of a 1960 article by Angus Campbell:

Abstract

The tides of party voting are as fascinating as the fluctuations of economic activity. Regularities in the ebb and flow of voting with the alternation of Congressional and Presidential elections challenge the analyst to find an explanation. This article seeks it in propositions rooted in survey data.

Campbell’s explanation was that presidential elections are largely driven by “short term forces” that provide a temporary advantage to one party, usually the winner of the presidency. Then in the midterm, with no presidential election, short term forces are less important and the electorate shrinks with lower turnout (a “low stimulus election” relative to presidential) and the “long-term force” of partisanship becomes relatively more dominant in the midterm. The result is a return to the partisan balance after the surge favoring the presidential winner two years earlier.

This is a beautifully elegant theory. It is rooted in a simple model of partisanship, short-term forces and the inevitable decline of turnout in midterms. I love it.

Alas, it no longer commands general acceptance as a theory of midterm seat loss. More emphasis is now given to presidential approval, economic conditions and incumbency. Those theories bring substantial empirical evidence, and are certainly sensible. But to me they lack Campbell’s beautiful simplicity.

I’m not here to argue theories of midterm loss, but rather to simply illustrate the votes side of midterm losses. That the president’s party almost always loses house seats in midterms is a fact. Here I look at the decline in votes for the president’s party from presidential to midterm.

For fun, I’m going to walk you through the puzzle and steps that end with the figure at the top of this post. Here is the first step. What IS this??

As my poor former students know, I enjoy starting a class example with a mystery. Show the chart above, invite speculation as to what it might be. I love this one because it looks like random noise with no relationship at all.

Next step: Revealing the variables.

OK here are the variables. National Democratic percentage of the 2-party House vote in the midterm by the national 2 party vote in the previous presidential election. Not much of a relationship. Some votes go up (above the diagonal) and about as many go down (below diagonal.)

Ahh, but what about control of the presidency? The midterm-loss of seats by the president’s party is well known. The national vote, here, shows the same pattern. Dems do better (above diagonal) with GOP president, and do worse with a Dem president, almost always (except 2002.)

This is the surge and decline of votes. Almost always the president’s party wins a smaller share of votes in the midterm than they did in the presidential year. Not surprisingly, fewer votes translate into fewer seats, but that’s not our topic here. For that see this post.

The pattern is clear if we fit a regression for midterms with Rep presidents (red line) and one for Dem pres (blue line). Now the upward slope is clear (midterm performance IS related to prior pres vote) and the party of president shifts the lines up (Rep pres) or down (Dem pres).

FWIW the red and blue lines are nearly parallel. A test of a pooled model finds the difference in slopes to be statistically insignificant (p=.9465). I’m using the separate regressions here, but there would be minimal difference for a pooled model.

So what does the model tell us about, say 2018? The red line estimates the Dem 2-pty vote in 2018 to be 53.1%, up from the Dem 2-pty 2016 vote of 49.5%. In fact, Dems got 54.4%, 1.3 points better than the model and 4.9 points over their 2016 performance.

We don’t know how Dems will do in 2022, but we do know how they did in 2020 and that there is a Dem president. The vertical black line shows the actual Dem share of 2020 House vote, and the blue arrow shows the fit: a predicted 47.8% in 2022, down from 51.6% in 2020.

This is the dilemma of every presidential party: they are almost certain to lose votes in midterm elections. For closely divided congresses (looking at you 117th) this imperils majorities. 2002 was an exception, with 1998 and 1990 almost being exceptions.

How do votes translate into seats? The relationship shifted after 1994 undoing a long standing Dem advantage. The votes-to-seats model expected Dems to hold 50.6% or 220 seats in 2021 (actual post-election was 222). For 2022 the estimate is 45.0% of seats. That would be 196 seats, a loss of 26 from the post-2020 election total.

The president’s party gained house seats in 1934, 1998 and 2002, and lost share of seats in every other midterm since 1862. Reps gained seats in 1902 as the House expanded but actually lost share of seats as Dems gained more that year.

If the historical pattern applies in 2022 the Democrats are unlikely to hold control of the House. In addition there will also be the effect of redistricting. Both parties will have an incentive to gerrymander for every advantage possible where they control the process.

Of course the past pattern may change. Political skill or folly might shift the balance away from the models. The model is useful because it gives us a basis for our expectations. We can judge party performance by whether outcomes exceed or fall short of model expectations. 12/12

Seats and Votes in the House

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How votes are converted to seats in the House of Representatives and how that has changed.

In a perfectly proportional legislature the percent of seats should equal the percent of votes received by a party. Electoral systems based on proportional representation come close to ensuring this by design.

Two-party, plurality, systems are rarely if ever proportional. They tend to reward votes disproportionately, giving more seats than votes to one party and fewer seats than votes to the other. They also often award a majority of seats for less than a majority of votes.

One measure of the bias in a system is the “representation ratio,” the percent of seats divided by percent of votes. A value over 1.0 means a party gets more seats share than votes share, and values less than 1.0 means underrepresentation.

In the US from 1942 until 1994 the Democratic party was advantaged, with a representation ratio typically around 1.1 with variation across elections. After 1994 that reversed, with the Republican party enjoying an advantage, a bit smaller than Dems had.

Part of this was the “solid South”, dominated by Democrats until the 1980s coupled with very low turnout which made winning Dem vote totals smaller than in competitive elections. The transformation of parties in the South after 1980 became a GOP advantage.

Gerrymandering also plays a role in the vote-to-seats relationship, with advantages to parties that control legislatures and governorships that create the districts. Courts imposed some limits on districting beginning in the 1960s.

From 1942 to 1994 Democrats were advantaged in all but two elections. Since 1994 Republicans have been advantaged in all but one election (2008). The advantages were persistent in each era.

The RepRatio is a simple measure of advantage, but what about how votes are converted to seats across elections? This chart shows the percent of seats won by percent of national vote won in each election. 1942-94 is different from 1996-2020.

One measure of bias is the percent of votes required to win 50 percent of seats. In 1942-94, Dems needed 48.4% of votes to reach 50% of seats. Since 1994, Dems need 51.2% of votes to reach a majority of the House. There is uncertainty but these are the expected outcomes.

Another measure is the “swing ratio”, the slope of the regression lines, measuring how much seat share changes for a 1 point change in vote share. In 1942-94 Dems got 1.80 percent more seats for a 1 percentage point increase in vote share. After 1994 it has been 1.47.

Post 1994 Republicans gained an advantage in votes required for half the seats & reduced the swing ratio to lessen the effect of votes on seats. Both eras have swing ratios over 1.0 meaning seats are more responsive to votes than pure proportionality. This is common in 2 party single-member district systems.

If we shift to the relationship between national presidential vote and seats in the House we can extend the time frame back to 1900. I divide into two partisan eras, 1932-1992 for Dems, and 1900-1928 plus 1996-2020 with a GOP House advantage.

Interestingly, the relationship of seats and votes is essentially the same for the 1900-28 and 1996-2020 eras of GOP advantage. A test of different slopes & intercepts gives p=.69 so I combine them here.

In the 1932-1992 Dem era, a Democratic presidential vote of just 36.3% was enough to expect a 50% Dem House. In the GOP eras, a Dem president needed 51.2% of the national vote to expect half of the House.

The Democratic solid South again provided a huge advantage in the 1932-92 period. In the two eras that Reps were advantaged in the House, their advantage is much smaller, requiring Dems to get 51.9% of the pres vote, 50.3 in 1900-28 & 52.7 since 1996.

The takeaway is that Republicans converted a long time disadvantage in winning House seats to a smaller but persistent advantage after 1994. Once control of the House was won in 1994, the GOP has held an advantage, despite one reversal in 2008.

The size of the current Democratic disadvantage is important, but it should be recognized that the GOP disadvantage from 1932-1994 was far greater. Changes in regional party dominance plays a big role in that and shows party advantage can be altered.