A plea to readers with two weeks until Election Day 2018 ends…

The 2018 midterm elections end in two weeks, on November 6, 2018.

I write “end” because early voting is underway in 28 states, including Massachusetts. In fact, it opened Monday, October 22, and so I dragged our two daughters to Brookline Town Hall so they could participate in the process. And, yes, I voted straight Democratic with the exception of governor.

The best habits start early as our youngest daughter’s backpack reveals.

I Voted sticker.JPG

Along those lines—as a former political-scientist-in-training, lifelong political junkie and huge fan of democracy, I cannot strongly encourage you enough to vote.


This plea applies both to my American readers and to my many international readers, whenever the opportunity next presents itself.


I do three things in this post.

  1. Update analyses of 2018 elections for the United States House of Representatives (“House”), United States Senate (“Senate”) and governor.
  2. Attempt to quantify the Republican polling “bounce” following the September 27, 2018 Senate Judiciary Committee testimony by Dr. Christine Blasey Ford and United States Court of Appeals Circuit Judge Brett M. Kavanaugh.
  3. Reconsider House, Senate and gubernatorial election projections under two scenarios: one where polls underestimate Republican voting by 3 percentage points, and where polls underestimate Democratic voting by 3 percentage points.


Updated analyses. As of Tuesday afternoon, October 23, 2018, the FiveThirtyEight forecast was that Democrats would win the national House vote by 8.9 percentage points. According to my “simple” model, that translates to an 89.8% probability Democrats net at least the 23 House seats they need to regain control of the House (projecting a 29 seat gain). By comparison, the FiveThirtyEight forecast is 85.8% and 40 seats—reasonably close to my less “complex” estimates.

Since I last wrote about Senate races, I created two new metrics.

  1. A weighted probability of Democratic victory
  2. A projected Democratic election day margin.

The victory probability is simply a weighted average of the “fundamentals” and adjusted polling average (APA) probabilities, with the latter increasing in weight based upon the number, recency and quality of published polls. I estimate the “fundamentals” probability by assuming a normal distribution whose standard deviation is that of my 3W-RDM measure (4.9), and I estimate the APA probability using a margin of error derived from the total sample size of all polls of each election conducted entirely in calendar year 2018, to which I add 3.0 to account for recent average polling bias (averaging across the last four elections in the table “Polling bias shifts from election to election”).

Weights are calculated using this formula:

#Polls/10 + #Sept/Oct Polls/2 + (Average Pollster Rating – 4.3) + %Sept/Oct Polls/10

For example, 51 total polls have been conducted since January 1, 2018 in the Florida Senate race, with 21 conducted since September 1, with an average pollster rating of 2.7 (using the letter-grade assigned by FiveThirtyEight on a scale where A+=4.3, A=4.0, etc.). Thus, the amount by which polls are weighted over fundamentals in this race is 51/10 + 21/2 + (2.7-4.3) + 41.2/10 = 5.1 + 10.5 – 1.6 + 4.1=18.1.

The “projected Democratic margin” is also the weighted average of the “fundamentals” and APA margins.

Table 1: Democratic Victory Probabilities and Margins in 10 Key 2018 Senate Elections

State Probability Democratic Victory Projected Democratic Margin Democratic Gain, Hold, Loss 3W-RDM
AZ 90.3% D+2.5 Gain R+9.7
FL 70.2% D+1.3 Hold R+3.4
IN 72.8% D+1.2 Hold R+16.3
MO 38.9% R+0.4 Loss R+15.9
MT 92.4% D+4.1 Hold R+18.6
NV 43.6% R+0.2 Hold D+2.0
ND 0.2% R+7.3 Loss R+29.4
TN 19.2% R+2.7 Hold R+25.8
TX 0.1% R+6.2 Hold R+15.3
WV 90.4% D+5.1 Hold R+35.5
  Lose 0.8 seats R+0.3 R+1 R+16.8

The rough-and-ready forecasts in Table 1 are consistent with anything from a Democratic loss of one seat to a Democratic gain of one seat, depending on outcomes of very close races in Missouri and Nevada (not to mention Florida, Indiana and, perhaps, Tennessee). In this, they are broadly in agreement with the FiveThirtyEight Senate forecast (19.0% chance Democrats regain Senate; average loss 0.5 seats), though they are far more bullish on Democratic chances in Missouri (61.1%), North Dakota (30.1%), Tennessee (24.5%) and Texas (21.5%), and more bearish on Arizona (63.4%).

Not to belabor the point, but given the extreme “redness” of these 10 states (16.8 percentage points more Republican than the nation, on average), even a net loss of “only” one Senate seat would be a moral victory of sorts for Democrats…though a net gain of two or more seats would be an actual victory, in that they would then control the Senate.

Table 2: Democratic Victory Probabilities and Margins in 19 Key 2018 Gubernatorial Elections

State Probability Democratic Victory Projected Democratic Margin Democratic Gain, Hold, Loss 3W-RDM
AK 18.8% R+2.3 Loss R+19.2
AZ 1.5% R+8.6 Hold R+9.7
CO 99.8% D+9.0 Hold D+2.2
CT 100.0% D+9.0 Hold D+12.8
FL 99.4% D+4.6 Gain R+3.4
GA 38.2% R+0.2 Hold R+9.6
IL 100.0% D+16.5 Gain D+14.7
IA 95.5% D+2.7 Gain R+4.7
KS 31.4% R+2.0 Hold R+23.4
ME 100.0% D+6.8 Gain D+5.9
MI 99.9% D+9.7 Gain D+2.2
MN 99.8% D+8.7 Hold D+1.5
NV 53.3% D+0.9 Gain D+2.0
NM 100.0% D+8.6 Gain D+6.5
OH 28.2% R+0.3 Hold R+5.8
OK 0.5% R+6.8 Hold R+38.1
OR 100.0% D+7.9 Hold D+8.7
SD 23.6% R+4.4 Hold R+25.8
WI 99.1% D+5.0 Gain D+0.7
AVE Gain 7.9 seats D+3.4 D+7 R+4.3

Table 2 presents Democratic victory probabilities and margins for those gubernatorial elections most likely to change partisan hands and/or with margin< 10 percentage points. This group of states is far more purple, averaging only 4.3 points more Republican than the nation as a whole.

The governor’s race in Alaska altered considerably on October 19, when Independent Governor Bill Walker suspended his reelection campaign and endorsed Democrat Mark Begich over Republican Mike Dunleavy, though the likely outcome (a Dunleavy win) remains the same. Otherwise, Democrats remain strongly favored to pick up governor’s mansions in Florida, Illinois, Iowa, Maine, Michigan, New Mexico and Wisconsin, losing only in Alaska (Walker was effectively a Democrat). Extremely close races in Georgia, Nevada and Ohio could go either way, while Democrats are within shouting distance in Kansas and South Dakota (albeit, with only two polls). At the same time, once-possible pickups in Arizona and Oklahoma now seem far less likely.

The bottom line (again, in broad agreement with FiveThirtyEight) is that Democrats appear poised to net between six and nine governor’s mansions, putting them tantalizingly close to a majority.

A Kavanaugh bounce? There is evidence of a pro-Republican bounce in polling following the sequence of events between the Judiciary hearings on September 27 and the final confirmation vote (50-48 in favor) on October 6, including the week-long FBI investigation, spurred by increased Republican enthusiasm and voting likelihood.

To quantify the bounce, I compared Senate and gubernatorial race polls, unskewed and weighted by pollster rating, conducted before (though after August 1) and after September 27; all polls had to be completed by September 26 or started no earlier than September 27.

Table 3: 2018 Polling Data in 16 Key 2018 Senate Elections, Before and After Ford-Kavanaugh Hearings 

State Adjusted Poll Average


Adjusted Poll Average




AZ D+3.0 (11) D+0.3 (8) -2.8 R+9.7
FL D+0.3 (14) D+2.1 (10) +1.9 R+3.4
IN D+1.9 (3) D+0.2 (8) -1.6 R+16.3
MI D+14.7 (9) D+12.4 (3) -2.3 D+2.2
MN D+5.9 (4) D+10.1 (3) +4.2 D+1.5
MS R+13.5 (1) D+1.4 (1) -14.9 R+18.5
MO R+1.6 (7) R+0.8 (7) -0.8 R+15.9
MT D+5.2 (6) D+3.7 (1) -1.5 R+18.6
NV D+0.2 (5) R+1.6 (5) -1.8 D+2.0
NJ D+7.2 (2) D+6.9 (5) -0.3 D+12.0
ND R+4.6 (1) R+12.9 (2) -8.3 R+29.4
OH D+12.2 (6) D+16.5 (2) +4.3 R+5.8
PA D+15.3 (7) D+14.4 (1) -0.9 R+0.4
TN D+0.3 (8) R+6.2 (5) -6.5 R+25.8
TX R+3.2 (10) R+7.0 (7) -3.8 R+15.3
WV D+8.2 (7) D+7.9 (4) -0.3 R+35.5
WI D+7.9 (4) D+9.7 (2) +1.8 D+0.7
AVE D+4.4 D+2.4 -2.0 R+10.4

On average across 17 key Senate races (Table 3), the Republican position in the polls improved by an average of 2.0 percentage points following the Ford-Kavanaugh hearings. And the more Republican the state, the more the Republican candidate’s position improved (r=0.48)—as can be seen in Arizona, Mississippi, North Dakota, Tennessee and Texas (and also, surprisingly, in Democratic-leaning Michigan and Nevada). In fact, removing six states where the Democrat is strongly favored (albeit, four won by Republican presidential nominee Donald Trump in 2016; average 3W-RDM D+1.7), the Republican increase jumps to 3.7 percentage points (D+1.2 to R+2.6; r=0.31). At the same time, the bounce fades (-0.6; r=0.41) once you examine only states with at least two polls in both time periods.

Table 4: Polling Data in Selected 2018 Gubernatorial Elections, Before and After Ford-Kavanaugh Hearings

State Adjusted Poll Average


Adjusted Poll Average




AK R+0.9 (2) R+11.8 (2) -10.9 R+19.2
AZ R+6.5 (9) R+14.5 (6) -8.0 R+9.7
AR R+36.7 (1) R+37.7 (1) +1.0 R+28.2
CA D+10.6 (7) D+11.4 (4) +0.8 D+23.2
CO D+9.1 (2) D+7.5 (1) -1.6 D+2.2
CT D+8.5 (4) D+5.7 (3) -2.8 D+12.8
FL D+4.6 (13) D+4.7 (7) +0.1 R+3.4
GA D+1.9 (3) R+1.8 (6) -3.7 R+9.6
IL D+15.1 (4) D+17.6 (2) +2.5 R+16.3
KS R+0.4 (3) R+0.1 (1) +0.3 R+23.4
ME R+0.6 (1) D+7.8 (2) +8.4 D+5.9
MD R+16.9 (3) R+18.7 (2) -1.8 D+22.6
MA R+36.5 (2) R+38.8 (1) -2.3 D+22.1
MN D+6.9 (4) D+10.5 (3) +3.6 D+1.5
MI D+11.0 (8) D+11.2 (2) +0.1 D+2.2
NV D+2.1 (2) R+0.9 (4) -3.0 D+2.0
NH R+12.7 (2) R+13.7 (3) -1.0 D+0.1
NY D+1.0 (1) D+22.7 (2) +21.7 D+21.6
OH R+2.0 (5) D+1.3 (2) +3.3 R+5.8
OR D+7.0 (2) D+5.1 (1) -1.9 D+8.7
PA D+15.8 (6) D+11.4 (1) -4.4 R+0.4
RI D+7.3 (1) D+9.9 (2) +2.6 D+18.0
SC R+7.8 (2) R+23.7 (1) -15.9 R+15.7
TN R+14.5 (7) R+18.4 (3) -3.9 R+25.8
TX R+17.0 (8) R+20.1 (4) -3.1 R+15.3
WI D+3.3 (6) D+4.6 (2) +1.3 D+0.7
AVE R+1.8 R+2.6 -0.8 R+1.1

Alabama, Idaho, Iowa, New Mexico, Oklahoma have no polls after September 26

Hawaii had no polls between August 1 and September 26.

The trend was similar in 26 governor’s races (Table 4; average R+1.1)—an overall Republican increase of 0.8 percentage points, though once you remove New York (only one extreme outlier poll between August 1 and September 26), the increase becomes 1.7 percentage points. Again, the sharpest increases were in more Republican states (r=0.43), especially Alaska, Arizona, Georgia, South Carolina, Tennessee and Texas (and, surprisingly, in purple-to-blue Connecticut, Nevada and Pennsylvania). Examining only states with at least two polls in both time periods, the Republican increase jumps to 1.5 percentage points (r=0.36).

So, the “Kavanaugh bounce” appears to have been roughly one-to-three percentage points, and it was most evident among Republican voters in Republican states—who may well have been “coming home” to their party anyway (the Ford-Kavanaugh hearings may only have started the process earlier). And there is evidence the bounce is fading somewhat—at least in House voting (which covers the entire nation rather than a Republican-leaning set of states). The FiveThirtyEight House forecast dropped from an 80.7% chance of a Democratic takeover on September 30 to 73.9% on October 4—but then started to increase again October 9. Similarly, the forecast was a 32.0% chance of a Democratic Senate takeover on September 30, but by October 11 the probability had dropped to 18.6%. After rising three percentage points since then, as of Tuesday afternoon, October 23, it stood at 18.9%; the gubernatorial forecast does not lend itself to an analogous comparison.

Alternate polling scenarios. That even a small Kavanaugh “bounce” was enough to reduce Democratic Senate and gubernatorial gains by one-to-two seats shows how close this election (or, at least, the binary outcome of “majority/minority status”) is.

This can be shown by increasing—or decreasing–every polling margin by three percentage points, consistent with the statistical “bias” polls have displayed in the last four even-numbered election years; the direction of that bias changes from year to year.

For the House, if the projected national Democratic margin in total vote was actually 5.9% (that is, a 7.0% election-to-election increase), the probability they regain control plummets to 25%, with an average net gain of only 20 seats, three fewer than necessary. By contrast, however, were the margin 11.9%, Democrats would be locks to regain House control (99.6% probability), netting an average of 40 seats. Put simply, this close to Election Day, Democrats could still fall achingly short of a House majority—or net as many as 20 more seats than necessary.

For the Senate, a pro-Democratic polling bias of three percentage points in the polls would result in losing seats in Florida, Indiana, Missouri and North Dakota, while gaining zero seats; this is the nightmare scenario for Democrats. And while a pro-Republican polling bias of “only” two percentage points would mean winning in Arizona, that would still be a net loss of three Senate seats.

By the same token, a pro-Republican polling bias of three percentage points would almost certainly give them majority status in the Senate, as they still lose Heidi Heitkamp’s seat in North Dakota while winning seats in Arizona, Nevada and (possibly after a recount) Tennessee.

That is, this close to Election Day, a range of losing four Senate seats and gaining two seats remains plausible for Democrats.

Finally, in governor’s races, Democrats appear to be far enough ahead in key states that even a pro-Republican polling bias of three percentage points would still net them five governor’s mansions (win in Florida, Illinois, Maine, Michigan, New Mexico, Wisconsin; lose in Alaska) with Iowa a virtual tie. But a pro-Democratic polling bias of three percentage points would truly unleash a blue gubernatorial tsunami: not only would they likely WIN in Alaska (and Iowa), they would most likely add Georgia, Kansas, Nevada, Ohio, Oklahoma and South Dakota to their column. An historic net gain of 13 governor’s mansions could easily be in the offing.


One overarching message from this barrage of data is that while pollsters do their best to model an unknown electorate and reduce uncertainty—the actual set of citizens who will turn out to vote remains, at best, a highly-educated guess and uncertainty (beyond just margin of error) still remains. Still, some good news for Democrats lies buried in a recent New York Times/Siena College poll. While the overall result was an eight percentage point lead for Republican Senator Ted Cruz (and among those whose certainty to vote is confirmed by prior voting behavior), Democratic challenger Beto O’Rourke actually LED by three percentage points among those who said they were almost certain to vote.

The other overarching message, then, is simply that every vote counts—even the tiniest changes in the composition of the 2018 electorate could fundamentally who governs us for the next two years.

I cannot say this often or loudly enough…PLEASE VOTE!

Until next time…

4 thoughts on “A plea to readers with two weeks until Election Day 2018 ends…

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