Three of the nation’s 99 state legislative chambers held regularly-scheduled elections for 220 seats on Nov. 2, 2021. In races where more than one candidate ran in the election, the average margin of victory was 23.6%. The margin of victory is the difference between the share of votes cast for the winning candidate and the second-place candidate in an election.
Major-party candidates won 46 seats by margins of 10% or less; Democrats won 24 of those seats Republicans won 22. That means that 21% of seats up for election were won by a margin of 10% or less.
Three races were decided by a margin of 0.5% or less. In New Jersey General Assembly District 11, the race was decided by a margin of 0.25% (347 votes). In Virginia House of Delegates District 91, the race was decided by a margin of 0.34% (94 votes). In Virginia House of Delegates District 85, the race was decided by a margin of 0.45% (127 votes).
Although there were more than double the seats up in the previous odd-year election, we can compare these numbers to 2019. The average margin of victory for the 538 seats up that year was 26.0%, with 57 seats (10.6%) decided by a margin of 10% or less. Two races that year were decided by a margin of 0.5% or less.
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