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2010 Senate · IL

Public Policy Polling · fieldwork ended 2010-10-15 (18 days before the election) · 557 respondents · IVR

The poll said

Democrat 40% · Republican 42%

R+2.0

The certified result

Democrat 46.42% · Republican 48.02%

R+1.6

The arithmetic

  1. Poll margin = 40 − 42 = -2.00
  2. Actual margin = 46.416 − 48.015 = -1.599
  3. Signed miss = -2.00 − (-1.599) = -0.401
  4. Absolute miss = |-0.401| = 0.401

The poll overstated the Republican by 0.4 points and had the right leader.

Where these numbers come from

Poll and result: 538 raw_polls.csv. Poll ID 32618, race ID 1518 (538 database).