Let’s take a look at Rasmussen’s final polls for the Senate races vs. the actual results to see if there is evidence of a systematic bias towards Republicans in their polling. I’m only looking at Senate races where there was a Rasmussen poll within the last month. There are some really obvious states (like Idaho & Vermont) where they didn’t bother polling in October.
State: Most Recent Rasmussen Poll vs. Actual Result = Difference
Hawaii: DEM +13 vs. DEM +54 = GOP +41
Nevada: GOP +4 vs. DEM +6 = GOP +10
Maryland: DEM +18 vs DEM +26 = GOP +8
Alaska: GOP +1 Vs IND +7 = GOP +8
California: DEM +3 vs. DEM +9 = GOP +6
West Virginia: DEM +4 vs. DEM +10 = GOP +6
Ohio: GOP +24 vs GOP +18 = GOP +6
Delaware: DEM +11 vs DEM +17 = GOP +6
Oregon: DEM +11 vs. DEM +16 = GOP +5
Colorado: GOP +4 vs. DEM +1 = GOP +5
New York (Schumer): DEM +28 vs DEM +33 = GOP +5
New York (Gillibrand): DEM + 21 vs. DEM +25 = GOP +4
Utah: GOP +33 vs GOP +29 = GOP +4
Conn.: DEM +7 vs DEM +10 = GOP +3
Indiana: GOP +18 vs GOP +15 = GOP +3
Pennsylvania: GOP +4 vs GOP +2 = GOP +2
Illinois: GOP +4 vs GOP +2 = GOP +2
Wisconsin: GOP +7 vs. GOP +5 = GOP +2
Washington: GOP +1 vs DEM +4 = GOP +5
Florida: GOP +20 vs. GOP +19 = GOP +1
Kentucky: GOP +12 vs. GOP +12 = Even
Arkansas: GOP +19 vs. GOP +21 = DEM +2
Missouri: GOP +9 vs GOP +13 = DEM +4
New Hampshire: GOP +17 vs. GOP +23 = DEM +6
Looking at this it seems quite obvious that Rasmussen has a significant bias towards the Republicans. Of these 24 polls, 20 had a lean towards the Republican, 1 was dead on, and 3 had a lean towards the Democratic candidate. The average lean was 4.9% points towards the Republican candidate.
In all 10 Senate elections decided by 10% points or less Rasmussen had a lean towards the Republican with the same average GOP bias of 4.9% points.
The Hawaii result is also interesting due to being off by such a huge amount. Was Rasmussen trying to to create a narrative of the Democrats struggling even in a deep blue state like Hawaii that happens to be the home state of the President? 538 says this 41% miss was the biggest one by any polling firm within the last 12 years.
I think it’s important to remember this bias during the next election cycle so that Rasmussen’s polling results include an asterisk for known GOP bias. I believe Rasmussen is in the business of narrative setting, and if their polls are known to be biased towards the GOP, they will be less successful in doing it.
I may have missed some October Senate polls, please let me know in the comments if you find any that I did not include.