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2010 Senate · IL

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

The poll said

Democrat 41% · Republican 44%

R+3.0

The certified result

Democrat 46.42% · Republican 48.02%

R+1.6

The arithmetic

  1. Poll margin = 41 − 44 = -3.00
  2. Actual margin = 46.416 − 48.015 = -1.599
  3. Signed miss = -3.00 − (-1.599) = -1.401
  4. Absolute miss = |-1.401| = 1.401

The poll overstated the Republican by 1.4 points and had the right leader.

Where these numbers come from

Poll and result: 538 raw_polls.csv. Poll ID 32641, race ID 1518 (538 database).