Here & Now

Redistricting: Maps Predict Election Results Accurately

Frederica Freyberg:

We’ve heard over and over that it’s easy for politicians to use a computer program to create legislative districts that favor Republicans or Democrats. Part of that is the parties already know where their supporters live and they can check past results to know which neighborhoods vote a certain way. But just how accurate are the new maps? “Here and Now”‘s Zac Schultz did the math and has the results.

Zac Schultz:

Secret documents unveiled during a redistricting lawsuit show when Republicans created the new legislative maps in 2011, they created a file for 59 assembly districts that had a Republican incumbent that year. For each new district they listed the percentage of the vote received by Republican candidates at the top of the ticket in certain elections since 2004, including Scott Walker and Attorney General JB Van Hollen in 2010, John McCain in 2008, Van Hollen in 2006 and President George Bush in 2004. We took the average of those five elections for each new assembly district and then compared it to the actual results in 2012. In the 55 races where a Republican-held seat had a Democratic challenger, the average prediction was off by just 7/10ths of a percent. In some cases, the prediction was even closer. In Keith Ripp’s 42nd assembly district, the computer model said the district would vote 56.55% Republican. Ripp received 56.58% of the vote, just 3/100ths of a percent difference. The computers were accurate in districts with overwhelming support, like the 52nd, where Representative Jeremy Thiesfeldt received 60.65% of the vote, just 5/100ths less than predicted. And they were accurate in razor-tight races as well, like the 93rd, where the average said that Republican Warren Petryk would receive 51.55% of the vote, and he received 7/10ths less than that. The models accurately predicted a Republican majority in the legislature, and a comfortable margin of victory as well. For the 53 Republicans they favored, they were expected to receive 58.4% of the vote. They actually received an average of 58.38%.