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2018 House · IL-16

Change Research · fieldwork ended 2018-10-28 (9 days before the election) · 554 respondents · Text-to-Web/Online Ad

The poll said

Democrat 41% · Republican 55%

R+14.0

The certified result

Democrat 40.88% · Republican 59.12%

R+18.2

The arithmetic

  1. Poll margin = 41 − 55 = -14.00
  2. Actual margin = 40.875 − 59.124 = -18.249
  3. Signed miss = -14.00 − (-18.249) = 4.249
  4. Absolute miss = |4.249| = 4.249

The poll overstated the Democrat by 4.2 points and had the right leader.

Where these numbers come from

Poll and result: 538 raw_polls.csv. Poll ID 56529, race ID 318 (538 database).