Latest CBS News YouGov Iowa poll finds Trump and Carson tied at 27, Bush 6, Oct. 15-22, 2015. Substantial plurality who say they won't change their mind are Trump supporters

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Carson 27
Trump 27
Cruz 12  
Rubio 9  
Bush 6  
Fiorina 3
Huckabee 2  
Jindal 2  
Kasich 2  
Santorum 2  
Christie 1

10/25/15, "CBS News 2016 Battleground Tracker, Iowa," YouGov

"Sample 529 Likely Republican Caucus Voters, conducted October 15-22, 2015, Margin of Error ±6.5%

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CBS News YouGov poll Methodology:

Online interviews of registered voters, some contacted by phone:

"The CBS News 2016 Battleground Tracker is a panel study based on interviews conducted on the internet of registered voters in Iowa, New Hampshire, and South Carolina. The poll was conducted by YouGov, an online polling organization.

The first wave was fielded between September 3-10, 2015, with 4860 respondents, and the second wave fieldwork was completed between October 15-22, 2015, with 3952 respondents, the majority of which are recontacts. Respondents were selected from YouGovs and two other online panels. These are “opt-in” panels which are open for anyone to join. However, YouGov also randomly selected persons from voter registration lists who had previously voted in primary elections and contacted them by phone. A total of 20017 registered voters were contacted by phone and the YouGov sample includes 1290 phone recruits." 

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Added: 32% of Iowa Trump supporters say they won’t change their mind. Only 15% of Carson supporters say they won't change their mind:

Poll dates, Oct. 16-19. Margin of error 4.9, 401 R caucus goers

10/23/15, "Bloomberg Politics Des Moines Register Iowa Poll," by Selzer and Co.

10/23/15, "Iowa Poll: Carson surges to 9-point lead; Trump slides," Des Moines Register, Jennifer Jacobs

"Only 15 percent of his (Carson's) backers say their mind is definitely made up. For Trump, a more substantial 32 percent say they won’t change their mind about him....  
 
Just 22 percent of (Iowa) Republican likely caucusgoers say their minds are made up; 78 percent say they could still be persuaded to support another candidate as their first choice."...

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