Princeton Election Consortium

A first draft of electoral history. Since 2004

When did partisan gerrymandering get worse, and why?

September 25th, 2017, 7:22am by Sam Wang


Partisan gerrymandering: when did it get worse, why, & what can courts & reformers do? New at The American Prospect, we trace the roots of an offense that has ballooned in recent decades.

Also, over at the Princeton Gerrymandering Project, we’ve added state legislative data. This includes data for the Wisconsin Assembly, which is important for next week’s Supreme Court case. Thanks to Rob Whitaker!

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A tutorial on partisan gerrymandering

September 7th, 2017, 8:45am by Sam Wang


Here’s a spiffy explainer video on how extreme partisan gerrymandering is committed, and how it can be detected by anyone who’s ever taken a basic statistics class.

Many thanks to the creatives behind this, Kyle McKernan and Danielle Alio of the Princeton University communications office. If you like their work, share it and “like” it!

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A Manageable Approach to Partisan Gerrymandering

September 4th, 2017, 2:22pm by Sam Wang


If the Supreme Court lays down a partisan symmetry-based standard for gerrymandering, will this open up a flood of lawsuits? Over at Election Law Blog, I use election evidence to argue that no, it will act as more of a brushback to future offenders.

The reason? As you can see in the chart, partisan gerrymanders only took off starting in the 2000 redistricting cycle, at the same time that it began to be thought that they were legal. Before then, they were considerably less common.

Thanks to Rick Hasen for hosting the essay, and to Brian Remlinger for data analysis.

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Amicus Brief in Gill v. Whitford

August 30th, 2017, 10:39pm by Sam Wang


Today we submitted our amicus brief (read the PDF) in the case of Gill v. Whitford. The authors are Heather Gerken, Jonathan N. Katz, Gary King, Larry Sabato, and me. In it, we argue that the Supreme Court should define basic fairness in redistricting using the concept of partisan symmetry. We use this idea to suggest simple statistical tests that could be used as a manageable standard to identify extreme partisan gerrymandering.

For example, are Democratic districts more packed than Republican districts than would be expected from inadvertent effects? That can be determined using Student’s t-test, the most common test in the sciences, invented by an experimental brewer at the Guinness Beer Company over 100 years ago.

If the Court accepts our recommendation, then there would be, for the first time, a way for courts to say when a partisan gerrymander has gone too far. This has been an unresolved issue since the mid-1980′s, when the Court first said that partisan gerrymandering was a violation of the U.S. Constitution. Now that partisan gerrymanders have become rampant in the last redistricting cycle, we believe it is time for the Supreme Court to act.

If you want to learn more about symmetry standards, I invite you to visit the Princeton Gerrymandering Project. You can also support our work here.

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Gerrymandering vs. Math: Who will win?

August 29th, 2017, 2:23pm by Sam Wang


From Emily Bazelon, a sharp look at partisan gerrymandering. Her thinking and analysis will resonate with fans of the Princeton Gerrymandering Project.

We’ll have more coverage soon, once the Supreme Court amicus filing deadline has passed…

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Democratic Partisan Gerrymanders, 1972-present

August 23rd, 2017, 12:39am by Sam Wang


The Princeton Gerrymandering Project makes it easy to browse all gerrymandering offenses for a given year. We are now starting to cross-reference these offenses with who had control over the redistricting process. It’s a daunting task, but our statistical analyst Brian Remlinger is on the case.

Brian has found something interesting: from 1972 until now, Democratic extreme partisan gerrymanders are surprisingly rare. What’s going on? [Read more →]

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Politics & Polls: Charlottesville and our broken public discourse

August 17th, 2017, 12:09pm by Sam Wang


The route between public outrage and consequences for President Trump seems quite broken. Why? Julian Zelizer and I chew it over in the new Politics & Polls. The opening is especially lively. Later we get into the regular nerdery.

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The Princeton Gerrymandering Project is live!

August 4th, 2017, 7:34am by Sam Wang


I am happy to announce our revamped site at gerrymander.princeton.edu. This is part of the Princeton Gerrymandering Project’s tooling up for the coming several years of work by courts and reformers.

The site now has an interactive map showing the results of three simple gerrymandering tests, applied in all the states. It allows you to upload data more conveniently than before. Finally, it has a tutorial, as well as links to background reading and current court cases. Check it out!

All of this was done by the team: Rob Whitaker, Brian Remlinger, Aimee Otsu, Sung Chang, and Naomi Lake. Hats off to their great effort.

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Partisan gerrymandering case to be argued before Supreme Court on October 3rd

July 19th, 2017, 2:22pm by Sam Wang


Just in: oral arguments in Gill v. Whitford will take place at 10:00am on Tuesday, October 3rd. It’s the second day of the fall term.

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Partisan Gerrymandering Across the 50 States

July 16th, 2017, 8:49am by Sam Wang


Note: I’ll pretty this up later. In the meantime, the files are available for you to download and inspect at the end of this post.

Over at the Associated Press, reporter David Lieb has published a new, in-depth analysis of the effects of gerrymandering in the 2016 Congressional and statehouse elections. The analysis found that the same states identified as partisan gerrymanders in 2012 and 2014 in my Stanford Law Review article — North Carolina, Michigan, Pennsylvania, and Maryland — also show clear signs of advantage to the same political paty.

The analysis is important for two reasons: (1) It means that the advantages built into the district maps in 2012 aren’t dissipating, and that these gerrymanders will likely hold up through the 2020 elections, and (2) These advantages aren’t an accident, because they are echoed at the level of state legislatures. In short, the parties that were in power in 2011 are likely to have a strong hand in drawing the maps again in 2021. They will go unfettered unless the opposing party gains the governorship*.

While the AP report primarily relies on the “efficiency gap” analysis, the Princeton Gerrymandering Project provided a separate t-test** analysis of election results for the article. The agreement between the two tests is striking. Virtually*** every state flagged by the t-test at the Congressional level is also flagged by the efficiency gap. Generally, we have found that the efficiency gap does well except for having a higher false-positive rate than the t-test, which is unsurprising since the t-test has such a venerable history. At the state legislative level, 4 of the 6 worst offenders according to the efficiency gap are also captured by the t-test with exceedingly low p-values.

The results of our analysis of Congressional races can be found here, and results for state house elections can be found here.

I thank Brian Remlinger and Naomi Lake for assistance with this post.

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*Currently, the opposition party holds the governor’s mansion in Pennsylvania (Tom Wolf, a Democrat) and Maryland (Larry Hogan, a Republican). Note that in North Carolina, the governor has no role in redistricting.

**A note on statistical testing: Our analysis used one- or two-tailed t-tests, depending on redistricting authority. For states with single party control of redistricting, we carried out one-tailed tests for advantage in the direction of that party. For states with bipartisan or nonpartisan redistricting, we carried out two-tailed tests.

***The exception is California, whose top-two primary system complicates analysis.

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