Did the Data Get it Right? The 2018 US Mid-term Elections

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Author: Rob Quirk
Posting date: 11/8/2018 11:17 AM
Over the past few weeks, every lawn, street corner, email, and blog post touted the mantra to get out and vote. The 2018 US mid-term elections drew more attention than ever, and data has its stamp on every element. 

With the Democrats taking the House, and the GOP increasing their hold on the Senate, both parties have claimed victory. But did things go as expected? For the details without the drama, it all comes down to what the data says.

What History Says


Voter registration, census taking, and good old-fashioned grass roots efforts across the country have fed information into the system. So, what did the numbers say? Let’s see what one of the most well-known poll tracking systems thought.

Data collected since the 1934 elections, according to the American Presidency Project at UC Santa Barbara, provides historical information on seat swings and seats defended in both the House and the Senate. Though approval ratings factor in, data is collected in aggregate, and takes no account of candidates, issues, or political conditions. This is the closest information may get to being truly nonpartisan.

Outside of this aggregation, two familiar factors also play a part, public assessment of the incumbent and the number of seats in Congress controlled by the President’s party. Though no matter which party the president favors, it has been historically proven, that their party loses seats and the opposite party gains seats. However, lower approval ratings usually mean more seats lost and the opposite party’s gain. 

Predictions for 2018 were generally accurate regarding the number of flipped seats, although Republican Senate gains did buck the trend. 

A Grass Roots Dive into House Races Across the US


Though results are often based on the sitting president’s impact on midterm elections, and the state of the national economy, it’s important to note that control ultimately depends on voters. In today’s midterm climate, grassroots efforts in over 400 districts, have taken shape and were key to the midterm results.

These key areas are shaped by five geographic regions collapsed into three “super regions”:

  • The West/East Coast Alliance
  • The New South/Heartland Alliance
  • The Blue-collar Midwest

Within these regions, four key indicators, which over the years have been the general consensus of where data might find its answers, also pointed in the direction we saw. 

Key indicators prior to the 2018 midterm election included:

  • Presidential approval rating
  • Congress' approval rating
  • Citizen’s satisfaction with the state of the union
  • Current economic conditions


All four indicators have strong statistical relationships with seat change for the president's party, such that when the indicators are worse, the president's party loses more seats. It may be the first and last of these that had the greatest impact in 2018, with a controversial President who leads a strong economy defining the campaign trail. 

As the next few weeks unfold, analysts will continue to look at the data, determining what it might mean for the 2020 Presidential election. However, with mixed results, the events of the next two years may still have a dramatic effect on what to expect. 

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