To get a great glimpse at how widely polls can vary, you only need to look at Michigan’s governor’s race this past week.
Since Oct. 20, four polls have emerged. Two are nearly identical, calling the race either a slight lead for Republican Gov. Richard Snyder or a statistical tie. The others have Snyder leading by either 8 or nearly 6 points over Democrat Mark Schauer, though the latter was within the margin of error and the former was on the edge of the margin of error.
How could they vary so much?
The two that show the race to be tied were automated polls that have more Democrats within their samples or showed higher Schauer support among Democrats. Either could have produced the seemingly closer race. The others, by EPIC MRA for the Detroit Free Press and WXYZ-TV, Channel 7 Detroit, and by Glengariff Group Inc. for The Detroit News and WDIV Channel 4 Detroit, were conducted by live interviewers and include samples that contained fewer self-identified Democrats.
Let’s look at them one by one:
- A poll by Mitchell Research & Communications for Fox 2 Detroit, had 86 percent of Democrats saying they’d vote for Schauer.
- A poll by Public Policy Polling conducted for the League of Conservation Voters, had 82 percent of Democrats voting for Schauer.
- Both were higher than the 79 percent that the EPIC MRA poll showed and the 79 percent that the Glengariff poll revealed.
All four polls had samples which included more Democrats than Republicans. But the EPIC MRA and Glengariff polls had the gap at 4 percentage points while the PPP poll stretched to 8 points and the Mitchell was at 4.6 points.
So with less than two weeks to the election, the polls don’t agree. Three have Snyder and Schauer within the margin of error, and the fourth showing Snyder with a comfortable lead.
What makes the differences so odd, is that for all their stark differences in the governor’s race, all four polls seem to agree that Democrat U.S. Rep. Gary Peters has a big lead over former secretary of state Terri Lynn Land in the race for U.S. Senate. EPIC MRA has Peters with a 9 point lead; Mitchell has it pegged at 13 points; PPP at 14 and Glengariff at 15 points.
As for who’s right, we’ll know Nov. 4.