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2008 House · IL-11

SurveyUSA · fieldwork ended 2008-10-20 (15 days before the election) · 623 respondents · IVR

The poll said

Democrat 50% · Republican 37%

D+13.0

The certified result

Democrat 58.40% · Republican 34.48%

D+23.9

The arithmetic

  1. Poll margin = 50 − 37 = 13.00
  2. Actual margin = 58.400 − 34.479 = 23.921
  3. Signed miss = 13.00 − (23.921) = -10.921
  4. Absolute miss = |-10.921| = 10.921

The poll overstated the Republican by 10.9 points and had the right leader.

Where these numbers come from

Poll and result: 538 raw_polls.csv. Poll ID 64334, race ID 4164 (538 database).