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2008 President · IL

Big Ten · fieldwork ended 2008-10-21 (14 days before the election) · 586 respondents · Live Phone

The poll said

Democrat 61% · Republican 32%

D+29.0

The certified result

Democrat 61.92% · Republican 36.78%

D+25.1

The arithmetic

  1. Poll margin = 61 − 32 = 29.00
  2. Actual margin = 61.918 − 36.781 = 25.137
  3. Signed miss = 29.00 − (25.137) = 3.863
  4. Absolute miss = |3.863| = 3.863

The poll overstated the Democrat by 3.9 points and had the right leader.

Where these numbers come from

Poll and result: 538 raw_polls.csv. Poll ID 16712, race ID 718 (538 database).