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2012 House · IL-17

GBAO · fieldwork ended 2012-10-17 (20 days before the election) · 450 respondents · Live Phone · partisan sponsor (DEM)

The poll said

Democrat 49% · Republican 45%

D+4.0

The certified result

Democrat 53.27% · Republican 46.72%

D+6.6

The arithmetic

  1. Poll margin = 49 − 45 = 4.00
  2. Actual margin = 53.275 − 46.718 = 6.557
  3. Signed miss = 4.00 − (6.557) = -2.557
  4. Absolute miss = |-2.557| = 2.557

The poll overstated the Republican by 2.6 points and had the right leader.

Where these numbers come from

Poll and result: 538 raw_polls.csv. Poll ID 51571, race ID 5044 (538 database).