How the AP-GfK poll on the 2016 campaign was conducted

No more than 1 time in 20 should chance variations in the sample cause the results to vary by more than plus or minus 2.5 percentage points from the answers that would be obtained if all adults in the U.S. were polled.

The margin of sampling error is plus or minus 2.7 percentage points for registered voters and plus or minus 2.9 percentage points for likely voters.