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2010 Governor · IL

Market Shares Corp. · fieldwork ended 2010-10-20 (13 days before the election) · 700 respondents · Live Phone

The poll said

Democrat 39% · Republican 43%

R+4.0

The certified result

Democrat 46.79% · Republican 45.94%

D+0.9

The arithmetic

  1. Poll margin = 39 − 43 = -4.00
  2. Actual margin = 46.789 − 45.935 = 0.854
  3. Signed miss = -4.00 − (0.854) = -4.853
  4. Absolute miss = |-4.853| = 4.853

The poll overstated the Republican by 4.9 points and had the wrong leader.

Where these numbers come from

Poll and result: 538 raw_polls.csv. Poll ID 32641, race ID 1285 (538 database).