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2008 President · IL

YouGov · fieldwork ended 2008-10-25 (10 days before the election) · 783 respondents · Online Panel

The poll said

Democrat 58% · Republican 39%

D+19.0

The certified result

Democrat 61.92% · Republican 36.78%

D+25.1

The arithmetic

  1. Poll margin = 58 − 39 = 19.00
  2. Actual margin = 61.918 − 36.781 = 25.137
  3. Signed miss = 19.00 − (25.137) = -6.137
  4. Absolute miss = |-6.137| = 6.137

The poll overstated the Republican by 6.1 points and had the right leader.

Where these numbers come from

Poll and result: 538 raw_polls.csv. Poll ID 16488, race ID 718 (538 database).