Illinois 12th

Lean R

2 in 7

Chance the Democrat wins (28.2%)

5 in 7

Chance the Republican wins (71.8%)

See the national overview

Forecasted turnout

Partisan lean

# How the forecast has changed

We'll be updating our forecasts every time new data is available, every day through Nov. 6.

Chance of winning

Popular vote share

KEY

AVERAGE

80% CHANCE OF FALLING IN RANGE

# What goes into the

classic forecast in the Illinois 12th

The Classic version of our model projects a race’s outcome by taking a weighted average of polls of a district (if available), polls of similar districts (CANTOR) and non-polling factors (fundamentals). It is then reverted toward a mean based on long-term trends in midterms and presidential approval ratings.

R+6.9
Adjusted polls
R+7.5
CANTOR
D+1.9
Fundamentals
R+5.6
Experts

R+6.9

Lite
R+3.8

Classic
R+4.4

Deluxe

<0.1
<0.1

Historical adjustment

Key

More weight

Less

#Latest polls

We've collected six polls for the Illinois 12th. We’re adjusting poll results in three ways: Polls of registered voters or all adults are adjusted to a likely-voter basis; older polls are adjusted based on shifts in the generic congressional ballot since the poll was conducted; and polls are adjusted for house effects (the tendency for a firm’s polls to lean toward Democrats or Republicans). Polls with larger sample sizes and those conducted by higher-quality polling agencies are given more weight, as are more recent polls.

								Adjustments
dates	pollster	sample		weight	Kelly	Bost	margin	likely voter	Time-line	House effects	Adjusted margin
Oct. 18-22 10/18-22	Siena College/New York Times	502	LV	1.51	39%	48%	R+8.5	—	<0.1	0.3	R+8.8
Oct. 3-7 10/3-7	Global Strategy Group D	404	LV	0.38	45%	46%	R+1.0	—	<0.1	1.9	R+3.0
Sep. 26-27 9/26-27	DCCC Targeting Team D	574	LV	0.31	43%	44%	R+1.5	—	0.1	2.9	R+4.5
Sep. 4-6 9/4-6	Siena College/New York Times	533	LV	0.04	43%	44%	R+1.0	—	0.1	0.3	R+1.4
Jul. 26-30 7/26-30	Global Strategy Group D	400	LV	0.00	41%	50%	R+9.0	—	0.7	1.9	R+10.3
Apr. 16-17 4/16-17	Public Policy Polling D	622	V	0.00	39%	44%	R+5.0	0.1	1.2	1.9	R+5.8

Weighted averageR+6.9

Key

A = adults

RV = Registered voters

V = voters

LV = likely voters

= partisan poll

#Similar districts and CANTOR

Our district similarity scores are based on demographic, geographic and political characteristics; if two districts have a score of 100, it means they are perfectly identical. These scores inform a system we use — CANTOR, or Congressional Algorithm using Neighboring Typologies to Optimize Regression — to infer what polling would say in unpolled or lightly polled districts, given what it says in similar districts.

Districts most similar to the Illinois 12th

	Sim. score	Polling avg.
IL-16	74	R+14.6
IL-13	74	R+5.4
OH-2	73	R+13.6
MI-2	72	R+8.0
OH-10	70	—
IN-2	69	—
MI-6	68	R+2.7
IL-17	68	—
KS-2	66	D+0.1
IN-9	66	R+7.6

#The “fundamentals”

The Classic and Deluxe versions of our model use several non-polling factors to forecast the vote share margin in each district.

Factor	Impact	Explanation
Incumbency	3.1	Mike J. Bost has been elected to 2 terms. Congress has only a 20.1% approval rating, reducing the incumbency advantage.
District partisanship	4.6	IL-12 is 13.2 percentage points more Republican-leaning than the country overall, based on how it has voted in recent presidential and state legislative elections. It voted for Trump in 2016 and Obama in 2012.
Incumbent's margin in last election	5.4	Bost won by 14.6 percentage points in 2016.
Generic ballot	6.8	Democrats lead by an average of 8.6 percentage points in polls of the generic congressional ballot.
Fundraising	5.7	As of Oct. 17, Brendan F. Kelly had raised $2,601,000 in individual contributions (73% of all such contributions to the major-party candidates); Bost had raised $964,000 (27%).
Incumbent's voting record in Congress	0.6	Bost has voted with Republicans 80% of the time in roll-call votes in recent sessions of Congress.
Challenger experience	1.9	Kelly has held elected office before. (So has Bost, but this is accounted for in our incumbency calculation.)
Scandals	0.0	Neither candidate is involved in a scandal.
Total	D+1.9

#Expert ratings

The Deluxe version of our model calculates an implied margin for each race based on expert race ratings from The Cook Political Report, Inside Elections and Sabato's Crystal Ball; it then adjusts that margin toward its estimate of the national political environment.

		Equivalent Margin
Expert	Rating	Raw	Adjusted
Cook Political Report	Lean R	R+6.7	R+6.1
Inside Elections	Tilt R	R+4.4	R+3.5
Sabato's Crystal Ball	Leans R	R+6.7	R+7.1
Average		R+5.9	R+5.6

How this forecast works

Nate Silver explains the methodology behind our 2018 midterms forecast. Read more …

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