Monday 5 November 2018

Senate Stats

Including two special elections in Minnesota and Mississippi, there are 35 senatorial elections this year. Because this is a much more manageable number than the 435 in the house, of state-wide importance and easier to poll than trying to phone around within congressional districts, there is far superior data to work with here. Most of these races have polling, and all but 4 published in the last month or less.


State Incumbent Rep Dem Polling Date
Arizona Republican 48 46 1.1% Nov 1-3
California Democrat No Republican Default N/A
Connecticut Democrat 35 58 -12.4% Oct 30-Nov 1
Delaware Democrat 24 61 -21.8% Sept 11-17
Florida Democrat 47 45 1.1% Nov 1-3
Hawaii Democrat    

Indiana Democrat 42 43 -0.6% Nov 1-3
Maine Independent 37 50 -7.5% Oct 27-29
Maryland Democrat 22 49 -19.0% Oct 1-6
Massachusetts Democrat 32 54 -12.8% Oct 25-28
Michigan Democrat 36 52 -9.1% Nov 1-3
Minnesota Democrat 33 53 -11.6% Nov 1-3
Minnesota (s) Democrat 39 49 -5.7% Nov 1-3
Mississippi Republican 57 31 14.8% Oct 13-18
Mississippi (s) Republican 50 36 8.1% Oct 13-18 (Run off)
Missouri Democrat 46 46 0.0% Nov 1-3
Montana Democrat 49 46 1.6% Nov 2-4
Nebraska Republican 54 39 8.1% Oct 23-27
Nevada Republican 46 45 0.5% Nov 1-3
New Jersey Democrat 39 51 -6.7% Oct 25-31
New Mexico Democrat 31 51 -12.2% Oct 26-Nov 1
New York Democrat 32 60 -15.2% Nov 1-3
North Dakota Democrat 51 42 4.8% Oct 27-30
Ohio Democrat 37 46 -5.4% Oct 29-30
Pennsylvania Democrat 39 56 -8.9% Nov 1-3
Rhode Island Democrat 36 55 -10.4% Oct 20-14
Tennessee Republican 49 49 0.0% Oct 28-31
Texas Republican 49 49 0.0% Nov 1-2
Utah Republican 59 23 22.0% Oct 3-9
Vermont Independent 30 66 -18.8% Oct 30-Nov 1
Virginia Democrat 36 52 -9.1% Sept 4-9
Washington Democrat 39 53 -7.6% Oct 4-9
West Virginia Democrat 42 47 -2.8% Oct 28-31
Wisconsin Democrat 44 53 -4.6% Oct 29-31
Wyoming Republican    


Dates above indicated date of publication for the polls. Only the most recent data is used. Where multiple surveys came out simultaneously, preference has been giver firstly to polls of likely voters over other data sets (registered voters, all adults etc.) and secondly to polls that account for third parties as there is no preferential vote in the US.

Delaware and Virginia do not have recent data, but the margins of past polls appear pretty decisive, especially in the former where Democrats performed almost three times better than Republicans. Hawaii and Wyoming do not have any recent, public polling, but probably don't need it. Hawaii hasn't elected a Republican since the 70s, consistently returning Democrats lately with over 60% of the vote. Wyoming is a little more mixed due to being a much older state but equally has not returned a Democrat since the 70s. Both are considered very safe for their respective parties. In fact in the rankings of ten separate companies, both seats are among many considered foregone conclusions. As with the house, we can easily take the median of these. The median is the preferable aggregation measure, as it does not require assigning precise numerical values to each category unlike averaging. Where the median lies between two rankings, the lesser is chosen to be safe unless that ranking is "tilt" due to the majority of sources not using that value.


State Incumbent Median Rating
Arizona Republican Tossup
California Democrat Safe Democrat
Connecticut Democrat Safe Democrat
Delaware Democrat Safe Democrat
Florida Democrat Tossup
Hawaii Democrat Safe Democrat
Indiana Democrat Tossup
Maine Independent Safe Indepenent
Maryland Democrat Safe Democrat
Massachusetts Democrat Safe Democrat
Michigan Democrat Likely Democrat
Minnesota Democrat Safe Democrat
Minnesota (s) Democrat Likely Democrat
Mississippi Republican Safe Republican
Mississippi (s) Republican Likely Republican
Missouri Democrat Tossup
Montana Democrat Lean Democrat
Nebraska Republican Safe Republican
Nevada Republican Tossup
New Jersey Democrat Lean Democrat
New Mexico Democrat Safe Democrat
New York Democrat Safe Democrat
North Dakota Democrat Lean Republican
Ohio Democrat Likely Democrat
Pennsylvania Democrat Likely Democrat
Rhode Island Democrat Safe Democrat
Tennessee Republican Lean Republican
Texas Republican Lean Republican
Utah Republican Safe Republican
Vermont Independent Safe Indepenent
Virginia Democrat Safe Democrat
Washington Democrat Safe Democrat
West Virginia Democrat Lean Democrat
Wisconsin Democrat Likely Democrat
Wyoming Republican Safe Republican

The latest polling and these rankings line up perfectly except in Montana (which came out while I was analysing this data)--something that should be unsurprising given the importance these rankings place on poll numbers. Below I have awarded seats with either a safe rating or a poll margin greater than 5%.


State Incumbent Rating Polling Prediction
Arizona Republican Tossup 1.1% TBC
California Democrat Safe Democrat Default Democrat
Connecticut Democrat Safe Democrat -12.4% Democrat
Delaware Democrat Safe Democrat -21.8% Democrat
Florida Democrat Tossup 1.1% TBC
Hawaii Democrat Safe Democrat None Democrat
Indiana Democrat Tossup -0.6% TBC
Maine Independent Safe Independent -7.5% Independent
Maryland Democrat Safe Democrat -19.0% Democrat
Massachusetts Democrat Safe Democrat -12.8% Democrat
Michigan Democrat Likely Democrat -9.1% Democrat
Minnesota Democrat Safe Democrat -11.6% Democrat
Minnesota (s) Democrat Likely Democrat -5.7% Democrat
Mississippi Republican Safe Republican 14.8% Republican
Mississippi (s) Republican Likely Republican 8.1% Republican
Missouri Democrat Tossup 0.0% TBC
Montana Democrat Lean Democrat 1.6% TBC
Nebraska Republican Safe Republican 8.1% Republican
Nevada Republican Tossup 0.5% TBC
New Jersey Democrat Lean Democrat -6.7% Democrat
New Mexico Democrat Safe Democrat -12.2% Democrat
New York Democrat Safe Democrat -15.2% Democrat
North Dakota Democrat Lean Republican 4.8% TBC
Ohio Democrat Likely Democrat -5.4% Democrat
Pennsylvania Democrat Likely Democrat -8.9% Democrat
Rhode Island Democrat Safe Democrat -10.4% Democrat
Tennessee Republican Lean Republican 0.0% TBC
Texas Republican Lean Republican 0.0% TBC
Utah Republican Safe Republican 22.0% Republican
Vermont Independent Safe Independent -18.8% Independent
Virginia Democrat Safe Democrat -9.1% Democrat
Washington Democrat Safe Democrat -7.6% Democrat
West Virginia Democrat Lean Democrat -2.8% TBC
Wisconsin Democrat Likely Democrat -4.6% TBC
Wyoming Republican Safe Republican None Republican

This leaves 11 races for further scrutiny: Arizona, Florida, Indiana, Missouri, Montana, Nevada, North Dakota, Tennessee, Texas, West Virginia and Wisconsin.

Some of these are resolved by looking at the polling over the last month. The tables below are dated at the last date of the polling period (to facilitate graphing later on) and only use polls of likely voters concluded on or after October 5:


Montana Rep Dem Polling
13/10/2018 38 47 -5.3%
18/10/2018 39 49 -5.7%
26/10/2018 45 48 -1.6%
30/10/2018 40 48 -4.5%
31/10/2018 42 49 -3.8%
1/11/2018 42 49 -3.8%
2/11/2018 42 50 -4.3%
3/11/2018 43 49 -3.3%
4/11/2018 49 46 1.6%


North Dakota Rep Dem Polling
19/10/2018 56 40 8.3%
24/10/2018 55 46 4.5%
30/10/2018 51 42 4.8%


Tennessee Rep Dem Polling
5/10/2018 50 42 4.3%
11/10/2018 54 40 7.4%
11/10/2018 47 44 1.6%
12/10/2018 52 48 2.0%
27/10/2018 51 46 2.6%
27/10/2018 51 45 3.1%
29/10/2018 49 45 2.1%
29/10/2018 44 44 0.0%
29/10/2018 53 47 3.0%
30/10/2018 50 41 4.9%
30/10/2018 52 44 4.2%
31/10/2018 49 49 0.0%


Texas Rep Dem Polling
5/10/2018 50 44 3.2%
5/10/2018 47 42 2.8%
9/10/2018 54 45 4.5%
11/10/2018 47 42 2.8%
13/10/2018 52 43 4.7%
13/10/2018 52 45 3.6%
14/10/2018 49 45 2.1%
18/10/2018 49 44 2.7%
21/10/2018 50 46 2.1%
21/10/2018 51 45 3.1%
26/10/2018 52 42 5.3%
28/10/2018 51 46 2.6%
28/10/2018 47 43 2.2%
30/10/2018 50 47 1.5%
2/11/2018 49 49 0.0%


West Virginia Rep Dem Polling
9/10/2018 40 41 -0.6%
13/10/2018 45 49 -2.1%
15/10/2018 47 53 -3.0%
18/10/2018 44 42 1.2%
19/10/2018 36 52 -9.1%
30/10/2018 40 45 -2.9%
31/10/2018 42 47 -2.8%


Wisconsin Rep Dem Polling
7/10/2018 43 53 -5.2%
18/10/2018 39 54 -8.1%
28/10/2018 43 54 -5.7%
31/10/2018 44 53 -4.6%

In most cases, earlier polling reinforces the current lean, often with larger margins. Wisconsin was the only "likely" rated seat not assigned above and this data concurs with the third-party rating. North Dakota is still a little short on data, but it is consistent and reaches back to a margin greater than 8%. These two states were nudging the 5% margin with their recent data anyway, and both seats have now been assigned along these lines. Things are a little fuzzier in Arizona, Florida, Indiana, Missouri and Nevada. These will be the five to watch tomorrow.


Arizona Rep Dem Polling
5/10/2018 44 47 -1.6%
10/10/2018 44 44 0.0%
17/10/2018 41 47 -3.4%
19/10/2018 48 46 1.1%
23/10/2018 52 45 3.6%
26/10/2018 44 47 -1.6%
26/10/2018 48 46 1.1%
27/10/2018 44 47 -1.6%
28/10/2018 47 45 1.1%
29/10/2018 47 51 -2.0%
29/10/2018 46 46 0.0%
30/10/2018 48 52 -2.0%
30/10/2018 48 43 2.7%
31/10/2018 49 42 3.8%
1/11/2018 48 42 3.3%
1/11/2018 47 50 -1.5%
2/11/2018 49 44 2.7%
3/11/2018 48 46 1.1%
3/11/2018 49 48 0.5%


Florida Rep Dem Polling
5/10/2018 46 44 1.1%
16/10/2018 49 47 1.0%
18/10/2018 51 46 2.6%
20/10/2018 45 50 -2.6%
20/10/2018 47 45 1.1%
21/10/2018 46 52 -3.1%
21/10/2018 41 49 -4.4%
21/10/2018 49 48 0.5%
21/10/2018 42 41 0.6%
22/10/2018 38 47 -5.3%
23/10/2018 45 49 -2.1%
23/10/2018 45 46 -0.5%
25/10/2018 44 49 -2.7%
26/10/2018 46 46 0.0%
26/10/2018 46 47 -0.5%
27/10/2018 44 48 -2.2%
28/10/2018 43 45 -1.1%
29/10/2018 48 50 -1.0%
29/10/2018 47 49 -1.0%
30/10/2018 47 49 -1.0%
30/10/2018 50 50 0.0%
30/10/2018 44 43 0.6%
31/10/2018 48 45 1.6%
31/10/2018 47 49 -1.0%
31/10/2018 49 45 2.1%
1/11/2018 59 45 6.7%
2/11/2018 48 46 1.1%
2/11/2018 48 50 -1.0%
2/11/2018 49 48 0.5%
2/11/2018 47 50 -1.5%
3/11/2018 47 45 1.1%


Indiana Rep Dem Polling
10/10/2018 44 40 2.4%
15/10/2018 45 55 -5.0%
16/10/2018 40 44 -2.4%
16/10/2018 40 41 -0.6%
17/10/2018 44 40 2.4%
20/10/2018 47 43 2.2%
26/10/2018 46 43 1.7%
27/10/2018 49 46 1.6%
28/10/2018 42 45 -1.7%
30/10/2018 38 45 -4.2%
30/10/2018 42 42 0.0%
31/10/2018 43 40 1.8%
1/11/2018 43 43 0.0%
2/11/2018 42 44 -1.2%


Missouri Rep Dem Polling
6/10/2018 44 42 1.2%
7/10/2018 45 44 0.6%
13/10/2018 50 47 1.5%
18/10/2018 47 46 0.5%
18/10/2018 49 42 3.8%
25/10/2018 49 45 2.1%
27/10/2018 49 46 1.6%
30/10/2018 43 43 0.0%
30/10/2018 44 46 -1.1%
31/10/2018 43 45 -1.1%
1/11/2018 43 46 -1.7%
2/11/2018 46 45 0.5%
2/11/2018 47 47 0.0%
3/11/2018 46 46 0.0%


Nevada Rep Dem Polling
10/10/2018 47 45 1.1%
12/10/2018 48 41 3.9%
15/10/2018 49 51 -1.0%
19/10/2018 47 41 3.4%
29/10/2018 45 48 -1.6%
31/10/2018 45 45 0.0%
26/10/2018 46 47 -0.5%
30/10/2018 43 46 -1.7%
1/11/2018 46 43 1.7%
1/11/2018 49 46 1.6%
2/11/2018 45 44 0.6%
3/11/2018 46 45 0.5%

Graphing this data does nothing to make any trends obvious, either.








Final Races

Arizona has not been represented by a Democrat since 1994, the only still living former senator for the state. Since then the retiring incumbent is the only one to have won with less than 50% of the vote, though this does indicate waning support from the heyday when the GOP would poll better than 70%. Trump won this state in 2016. 10 of the 17 likely-voter (LV) polls in the last month not resulting in a tie and 6 of the 8 surveys in the past week favour the Republicans, and the average of the margins is 0.4% to the Republicans.
Prediction: Republican retain.

Florida has a recent mixed history, with the running incumbent a Democrat having held his seat since the 2000 election, but his Class 3 colleagues in that time have included three Republicans--currently former Presidential candidate Marco Rubio. Trump won this state in 2016. The Floridian plot above is the least confused, slight apparent favour to the Democrats, and the only rating organisation not to call it a tossup favoured the Dems only marginally. Of the whopping 31 LV polls in the last month, 16 were won by the Dems and 2 were ties, leaving only 13 for the GOP. The average margin was -0.3%, the barest lean to the Dems. Yet of the 11 un-tied polls in the last week, the Republicans have won 7 including the largest margin in the sample on Nov 1. The average margin over that period was 0.8% in their favour. If this blog still awarded tossups, this would be a perfect case.
Prediction: Republican Win, but this is little better than a coin flip.

Indiana is another mixed state, although two years ago the Republicans won 52:42 in the class 3 senate race and Trump also carried the state. In the last month, 14 LV polls were conducted. The Democrats won 6, the Republicans 6 and two were tied. Both of those ties came in the past week, along with 2 Dem wins and a single Rep win, though this followed a week and a half of strong Republican polling. The average margin over the month is -0.2%, hinting at a slight Democrat lean. This increase to -0.7% over the last week. The only rating not to classify Indiana a tossup gave the Dems a slight edge too.
Prediction: Democrat Retain, but dubious.

Missouri has another mixed history, and two years ago the GOP won by a narrow 49:46 margin as well as in the presidential race. There have been 14 LV polls in the last month, and the Republicans have won 8, with another three tossups. All three tossups came in the past week, as did every survey favouring the Dems indicating a narrowing lead. The Republicans have only led one poll this week despite their strong start. The average margin over the month may have been 0.6% favouring the state turning red, but this last week that has been -0.5%. I can't tell if this is volatile data, if the early numbers were off, if the recent numbers are unreliable or if there has been a flip in opinions despite no real reduction in the Rep polling prior to the shift to Democrat support or increase in the blue vote since. I have to assume the numbers are good and something happened to voters around the 28th or 29th to cause this shift, but who knows if that's accurate.
Prediction: Democrat Retain

Nevada, perhaps unsurprisingly for yet another close seat and the last to be predicted, has another mixed history. The senatorial elections since 1998 have alternated red and blue, with the class 3 senators being consistent Democrats and the Class 1 senators--those up for reelection in 2018--being Republican. Dems won 47:45 in 2016, as did the Clinton vote. Of the 12 LV polls this month, the Republicans won 7, and another was a tie. This includes 4 of the 5 polls this week. The monthly and weekly margins favoured the Republicans as a result, at 0.7% and 0.5% respectively.
Prediction: Republican Retain

Concluding Prediction:


State Incumbent Prediction
Arizona Republican Republican
California Democrat Democrat
Connecticut Democrat Democrat
Delaware Democrat Democrat
Florida Democrat Republican
Hawaii Democrat Democrat
Indiana Democrat Democrat
Maine Independent Independent
Maryland Democrat Democrat
Massachusetts Democrat Democrat
Michigan Democrat Democrat
Minnesota Democrat Democrat
Minnesota (s) Democrat Democrat
Mississippi Republican Republican
Mississippi (s) Republican Republican
Missouri Democrat Democrat
Montana Democrat Democrat
Nebraska Republican Republican
Nevada Republican Republican
New Jersey Democrat Democrat
New Mexico Democrat Democrat
New York Democrat Democrat
North Dakota Democrat Republican
Ohio Democrat Democrat
Pennsylvania Democrat Democrat
Rhode Island Democrat Democrat
Tennessee Republican Republican
Texas Republican Republican
Utah Republican Republican
Vermont Independent Independent
Virginia Democrat Democrat
Washington Democrat Democrat
West Virginia Democrat Democrat
Wisconsin Democrat Democrat
Wyoming Republican Republican

This prediction sees the Republicans take two states: Florida and North Dakota. Indiana is also in the firing line. This would raise the Republican majority from a single seat to three or four, securing a reliable Senate even if the Dems to reclaim the lower house.
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