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2010 Senate · IL

Public Policy Polling · fieldwork ended 2010-10-30 (3 days before the election) · 814 respondents · IVR

The poll said

Democrat 42% · Republican 46%

R+4.0

The certified result

Democrat 46.42% · Republican 48.02%

R+1.6

The arithmetic

  1. Poll margin = 42 − 46 = -4.00
  2. Actual margin = 46.416 − 48.015 = -1.599
  3. Signed miss = -4.00 − (-1.599) = -2.401
  4. Absolute miss = |-2.401| = 2.401

The poll overstated the Republican by 2.4 points and had the right leader.

Where these numbers come from

Poll and result: 538 raw_polls.csv. Poll ID 32802, race ID 1518 (538 database).