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Chance the Democrat wins (14.3%)
Chance the Republican wins (85.7%)
We'll be updating our forecasts every time new data is available, every day through Nov. 6.
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.
We've collected eight polls for the Iowa 4th. 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.
|margin||likely voter||Time-line||House effects||Adjusted margin|
Oct. 31-Nov. 4
|Siena College/New York Times||423||LV|
Oct. 29-Nov. 1
A = adults
RV = Registered voters
V = voters
LV = likely voters
= partisan poll
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.
|Sim. score||Polling avg.|
The Classic and Deluxe versions of our model use several non-polling factors to forecast the vote share margin in each district.
|Steve King has been elected to 8 terms. Congress has only a 20.1% approval rating, reducing the incumbency advantage.|
|IA-4 is 22.5 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 Romney in 2012.|
|Incumbent's margin in last election|
|King won by 22.5 percentage points in 2016.|
|Democrats lead by an average of 8.6 percentage points in polls of the generic congressional ballot.|
|As of Oct. 17, J.D. Scholten had raised $1,585,000 in individual contributions (75% of all such contributions to the major-party candidates); King had raised $528,000 (25%).|
|Incumbent's voting record in Congress|
|King has voted with Republicans 86% of the time in roll-call votes in recent sessions of Congress. Candidates who vote with their party very frequently tend to underperform at the ballot booth, other factors held equal.|
|Scholten has never held elected office.|
|Neither candidate is involved in a scandal.|
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.
|Cook Political Report||R+6.7||R+6.1|
|Sabato's Crystal Ball||R+6.7||R+7.1|
Nate Silver explains the methodology behind our 2018 midterms forecast. Read more …