Five Senate and 44 House races in 2018 were decided by less than 5 percent

The average margin of victory in the 2018 elections was the smallest it had been in even-year congressional races since 2012.
 
Margin of victory—or MOV—is the difference between the share of votes cast for the winning candidate and the share cast for the losing one.
 
Since it is June, the sixth month of the year, here are six more quick facts from our research:
 
  • Sixty-nine percent of 2018’s congressional races were decided by a margin of more than 15 percentage points.
  • In 2018’s 33 regularly-scheduled U.S. Senate elections, the average MOV was 16.8%. This was the smallest average since 2012 when that year’s Senate races averaged a 20% MOV.
  • Republican candidates who won Senate races had an average MOV of 14.3%, compared to an MOV of 16.8% in races won by Democratic candidates. Seventeen Senate races (more than half) were decided by a margin of victory greater than 15%.
  • The closest Senate race was in Florida, where then-Gov. Rick Scott (R) defeated incumbent Bill Nelson (D) by a margin of 0.12%—10,003 votes out of 8.2 million cast. The largest MOV was in Hawaii, where incumbent Mazie Hirono (D) won by 42.3%.
  • In 434 U.S. House elections, the average margin of victory was 30.2%. This was the smallest average since 2012 when the average MOV was 31.8%. Republican candidates who won did so by an average margin of 22.8%. The average margin in House races won by Democrats was 36.6%.
  • The closest House race was in Georgia’s 7th Congressional District where incumbent Rob Woodall (R) defeated Carolyn Bourdeaux (D) by 433 votes—a margin of 0.15%.
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About the author

David Luchs

David Luchs is a staff writer at Ballotpedia and can be reached at david.luchs@ballotpedia.org

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