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2018 House · PA-18

Gravis Marketing · fieldwork ended 2018-03-03 (10 days before the election) · 911 respondents · IVR/Online Panel

The poll said

Democrat 42% · Republican 45%

R+3.0

The certified result

Democrat 49.86% · Republican 49.53%

D+0.3

The arithmetic

  1. Poll margin = 42 − 45 = -3.00
  2. Actual margin = 49.863 − 49.533 = 0.330
  3. Signed miss = -3.00 − (0.330) = -3.330
  4. Absolute miss = |-3.330| = 3.330

The poll overstated the Republican by 3.3 points and had the wrong leader.

Where these numbers come from

Poll and result: 538 raw_polls.csv. Poll ID 51024, race ID 1759 (538 database).