The Mitchell poll results did show Sanders leading Clinton, 58% to 39%, with 18- to 39-year-olds.
Mitchell said Tuesday results will make his firm reevaluate its methods and use some form of digital polling to reach more young voters who use cell phones before a slew of primaries arrive next Tuesday.
"I'm not going to go into the method we'll use next week, but we will use digital and phone polling and try to pick it right, especially for the Dems," Mitchell said. "We have to capture millennials better that we did yesterday. Being wrong is unacceptable."
Mitchell said his firm will use a technique it has relied on with commercial clients, possibly one that allows a voting survey to reach a mobile device that involves geo-fencing. With geo-fencing, a pollster can know if the device is actually located within the voting district. That would protect from situations where a phone has an area code in a voting state, but is being used elsewhere.
The well-regarded Monmouth University poll in the Michigan primary found on Monday that Clinton had a 13-point advantage over Sanders. That poll actually relied on reaching out to 704 likely voters from both major parties, including 260 who had cell phones as well as 444 who used land line phones. But only 302 of that 704 were likely Democratic voters, and it isn't clear how many of them were using cell phones.
Patrick Murray, the pollster behind the Monmouth polls, could not be reached for comment.
After at least 13 pollsters in January predicted Donald Trump would top the Iowa Republican caucuses, Texas Sen. Ted Cruz won instead.
As with Michigan, the question of voters with cell phones was raised by experts in Iowa for what happened.
"Polling as a whole is becoming more challenging as it gets more difficult to reach voters in a random manner and keep them engaged for a full survey," GOP media consultant Brad Todd told USA Today in early February. "Most media and university surveys are cheap and use methodological shortcuts that make them even more error-prone."
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