Poll Analysis: Democrats make gains

Senate Democrats*	Senate Republicans
39.2% probability	60.8% probability
Mean of 49 seats	Mean of 51 seats

Saturday’s analysis showed control of the Senate to likely remain in the hands of the Republicans. The Democrats had only a 12.1% probability of taking the Senate. I’ve added about 20 new polls since then. I’ve also shortened the “current poll” window to 10 days (if only to match the Presidential election).

Two days later, after 100,000 simulated elections, Democrats have a Senate majority 12,350 times, there were 26,823 ties), and Republicans control the Senate 60,827 times. In other words, Democrats have a 39.2% probability of controlling the Senate and Republicans have a 60.8% probability of controlling the Senate.

There has been a few interesting changes.

• Florida: Democrat Patrick Murphy is trying to oust Sen. Marco Rubio (R). Rubio has held the lead in recent polls, but his margins have shrunk. Rubio’s chances have shrunk from near certainty to a 96% probability. This is still quite good, of course.
  

• Missouri: Democrat Jason Kander is going after Sen. Roy Blunt’s (R) seat. We lose three old polls and gain two new ones for a total of 6 polls. Two are tied; Blunt leads by small margins in three polls. One poll has Kander up by +0.7%. This has shifted the Democrat’s chances from 6.6% to 42.9%.
  

• Nevada: We have 2 current NV polls in the open seat race between Catherine Cortez Masto (D) and Joe Heck (R). The most recent poll has Cortez Masto up +1%; the other poll has Heck up by +2%. So The Democrat’s chances have risen from 7% to 43%.

  

• New Hampshire: The state is just close, close, close. Of 7 current polls Sen. Kelly Ayotte (R) leads by small margins in four, and Maggie Hassan (D) leads by small margins in three. The analysis suggests Hassan has a 33% chance of taking the seat.

  

• North Carolina: This is another very close state. The four current polls give two to Sen. Richard Burr (R) and one to Deborah Ross (D); the last one is a tie. Consequently, Burr’s chances of keeping his seat has dropped from 85% to 72%.

  

• Wisconsin: This is the only significant gain for Republicans. Democrat Russ Feingold has been leading Sen. Ron Johnson (R) for the great majority of polls. The three “current” polls have Feingold up, but with smaller margins than the past (+1%, +2%, and +3%). Johnson’s chances have increased from 14% last Saturday to 22% now.

  

Here is the distribution of Senate seats from the simulations:^*

This graphs shows the probability of at least each number of seats controlled by the Democrats:^*

• 100000 simulations: Democrats control the Senate 39.2%, Republicans control the Senate 60.8%.
• Average ( SE) seats for Democrats: 49.2 ( 1.1)
• Average (SE) seats for Republicans: 50.8 ( 1.1)
• Median (95% CI) seats for Democrats: 49 (47, 51)
• Median (95% CI) seats for Republicans: 51 (49, 53)

Expected outcomes from the simulations:

• Democratic seats w/no election: 35
• Independent seats w/no election: one
• Republican seats w/no election: 30
• Contested Democratic seats likely to remain Democratic: nine
• Contested Republican seats likely to remain Republican: 21
• Contested Democratic seats likely to switch: one
• Contested Republican seats likely to switch: three

This table shows the number of Senate seats controlled for different criteria for the probability of winning a state:^* Safe>0.9999, Strong>90%, Leans>60%, Weak>50%

Threshold	Safe	+ Strong	+ Leans	+ Weak
Safe Democrat	43
Strong Democrat	4	47
Leans Democrat	1	1	48
Weak Democrat	0	0	0	48
Weak Republican	1	1	1	52
Leans Republican	4	4	51
Strong Republican	5	47
Safe Republican	42

This table summarizes the results by state. Click on the poll number to see the individual polls included for a state.

		#	Sample	%	%	Dem	Rep
State	@	polls	size	Dem	Rep	% wins	% wins
AL		0	0			(0)	(100)
AK		1&	320	23.4	76.6	0.0	100.0
AZ		6	4147	43.6	56.4	0.0	100.0
AR		1&	608	38.2	61.8	0.0	100.0
CA		1	552	63.4	36.6	100.0	0.0
CO		3	1681	54.3	45.7	99.3	0.7
CT		1&	872	61.7	38.3	100.0	0.0
FL		4	2739	47.6	52.4	3.7	96.3
GA		3	2008	44.1	55.9	0.0	100.0
HI		0	0			(100)	(0)
ID		1&	823	29.5	70.5	0.0	100.0
IL		1	450	60.0	40.0	99.9	0.1
IN		2	884	48.3	51.7	23.6	76.4
IA		3	1804	37.1	62.9	0.0	100.0
KS		1	535	36.4	63.6	0.0	100.0
KY		1&	566	41.5	58.5	0.2	99.8
LA		1&	794	34.6	65.4	0.0	100.0
MD		1&	614	66.6	33.4	100.0	0.0
MO		6	4595	49.0	51.0	17.1	82.9
NV		2	1332	49.6	50.4	42.9	57.1
NH		7	4312	49.5	50.5	32.6	67.4
NY		1	567	72.8	27.2	100.0	0.0
NC		4	2777	49.2	50.8	28.2	71.8
ND		0	0			(0)	(100)
OH		3	2342	38.6	61.4	0.0	100.0
OK		0	0			(0)	(100)
OR		1&	558	62.7	37.3	100.0	0.0
PA		8	4945	52.4	47.6	99.3	0.7
SC		1&	941	38.4	61.6	0.0	100.0
SD		1&	534	39.3	60.7	0.1	99.9
UT		2	778	28.7	71.3	0.0	100.0
VT		1&	559	69.1	30.9	100.0	0.0
WA		1	641	56.8	43.2	99.2	0.8
WI		3	2778	51.0	49.0	78.1	21.9

^@ Current party in office
^& An older poll was used (i.e. no recent polls exist).
^*Analysis assume that the two independent candidates will caucus with the Democrats.

Details of the methods are given in the FAQ.