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2018 House · IL-13

The New York Times/Siena College · fieldwork ended 2018-10-23 (14 days before the election) · 501 respondents · Live Phone

The poll said

Democrat 40.97% · Republican 46.08%

R+5.1

The certified result

Democrat 49.62% · Republican 50.38%

R+0.8

The arithmetic

  1. Poll margin = 40.97 − 46.08 = -5.11
  2. Actual margin = 49.619 − 50.378 = -0.759
  3. Signed miss = -5.11 − (-0.759) = -4.351
  4. Absolute miss = |-4.351| = 4.351

The poll overstated the Republican by 4.4 points and had the right leader.

Where these numbers come from

Poll and result: 538 raw_polls.csv. Poll ID 56445, race ID 315 (538 database).