The Star Tribune and Minnesota Public Radio News polled 800 Minnesota likely voters between Sept. 10 and Sept. 12, on a number of topics, including Special Counsel Robert Mueller's investigation into possible collusion with Russia during the 2016 presidential election. Highlights from the question about whether the probe is fair or not are below. Scroll down the page to see details about how the poll was conducted and the demographics of the 800 respondents.

Sept. 21 poll analysis Previous poll results Methodology

To date, do you think Special Counsel Robert Mueller's investigation into possible collusion with Russia has been fair and impartial, or do you think it has been unfair and biased against President Trump?

Fair Biased Not sure 53% 31% 16% Fair Biased Not sure Men 50% 36% 14% Women 55 28 17 Democrats 87 4 9 Republicans 14 71 15 Independents / other 51 25 24 18-34 67 22 11 35-49 52 29 19 50-64 49 34 17 65+ 48 38 14 Under $50,000 46 35 19 $50,000 and over 53 32 15 Hennepin / Ramsey 64 24 12 Metro Suburbs 46 36 18 Southern Minn. 54 30 16 Northern Minn. 44 39 17 Trump voters 14 69 17 Clinton voters 88 1 11 About the poll

This Star Tribune/MPR News Minnesota Poll findings are based on interviews conducted Sept. 10-12 with 800 Minnesota likely voters. The interviews were conducted via land line (60 percent) and cellphone (40 percent). The poll was conducted for the Star Tribune and Minnesota Public Radio News by Mason-Dixon Polling and Research Inc. Results of a poll based on 800 interviews will vary by no more than 3.5 percentage points, plus or minus, from the overall population 95 times out of 100. Margins are larger for groups within the sample, such as Democrats and Republicans, and age groups.

The self-identified party affiliation of the respondents is 37 percent Democrats, 31 percent Republicans and 32 percent independents or other.

Sampling error does not take into account other sources of variation inherent in public opinion surveys, such as nonresponse, question wording or context effects. In addition, news events may have affected opinions during the period the poll was taken.

Readers can e-mail questions to djmcgrath@startribune.com.

Demographic breakdown of this polling sample

PARTY DFL/Democrat 299 (37%) Republican 246 (31%) Independent/Other 255 (32%) AGE 18-34 152 (19%) 35-49 200 (25%) 50-64 226 (28%) 65+ 216 (27%) Refused 6 (1%) GENDER Male 377 (47%) Female 423 (53%) INCOME < $25,000 84 (10%) $25,000-$49,999 127 (16%) $50,000-$74,999 130 (16%) $75,000-$99,999 121 (15%) $100,000+ 125 (16%) Refused 213 (27%) REGION Hennepin/Ramsey 255 (32%) Metro Suburbs 230 (29%) Southern Minnesota 160 (20%) Northern Minnesota 155 (19%) INTERVIEW Land-line 483 (60%) Cell Phone 317 (40%)