But remember: It’s just one poll, and we talked to only 423 people. Each candidate’s total could easily be five points different if we polled everyone in the district. And having a small sample is only one possible source of error.

Will an incumbent’s words catch up with him? We made 14636 calls, and 423 people spoke to us.

This survey was conducted by The New York Times Upshot and Siena College.

Hey, I’m Alex Burns, a politics correspondent for The Times. I’ll give you the latest reporting and intel on the midterms and take your questions from the campaign trail.

It’s generally best to look at a single poll in the context of other polls:

Mr. Scholten, a paralegal, has outraised Mr. King by about $1.7 million to $700,000. He has been barnstorming all 39 of the district’s counties in a Winnebago, stressing his longtime local roots and positioning himself as a centrist on issues like gun control and abortion. On health care, he has joined Bernie Sanders’s call for Medicare for all, and Mr. Sanders campaigned with him last week.

Mr. King has a history of inflammatory language on issues like race and immigration, yet his seat in this rural, strongly Republican district has long been seen as safe. The mass shooting at a Pittsburgh synagogue over the weekend has prompted a new look at the anti-Semitic subtext of some of his remarks and retweets , and there have been calls for consumer boycotts on companies that have donated money to his campaign. On Tuesday, he was denounced by the chairman of the National Republican Congressional Committee.

If sampling error were the only type of error in a poll, we would expect candidates who trail by five points in a poll of 423 people to win about one out of every six races. But this probably understates the total error by a factor of two .

One reason we’re doing these surveys live is so you can see the uncertainty for yourself.

As we reach more people, our poll will become more stable and the margin of sampling error will shrink. The changes in the timeline below reflect that sampling error, not real changes in the race.

Our turnout model There’s a big question on top of the standard margin of error in a poll: Who is going to vote? It’s a particularly challenging question this year, since special elections have shown Democrats voting in large numbers. To estimate the likely electorate, we combine what people say about how likely they are to vote with information about how often they have voted in the past. In previous races, this approach has been more accurate than simply taking people at their word. But there are many other ways to do it. Our poll under different turnout scenarios Who will vote? Est. turnout Our poll result The types of people who voted in 2014 272k King +9 People whose voting history suggests they will vote, regardless of what they say 285k King +6 Our estimate 288k King +5 People who say they will vote, adjusted for past levels of truthfulness 303k King +3 People who say they are almost certain to vote, and no one else 325k King +7 The types of people who voted in 2016 350k King +10 Every active registered voter 467k King +5 Just because one candidate leads in all of these different turnout scenarios doesn’t mean much by itself. They don’t represent the full range of possible turnout scenarios, let alone the full range of possible election results.

The types of people we reached Even if we got turnout exactly right, the margin of error wouldn’t capture all of the error in a poll. The simplest version assumes we have a perfect random sample of the voting population. We do not. People who respond to surveys are almost always too old, too white, too educated and too politically engaged to accurately represent everyone. How successful we were in reaching different kinds of voters Called Inter-

viewed Success

rate Our

respon­ses Goal 18 to 29 1 3 3 3 4 6 1 in 29 11% 10% 30 to 64 6 0 5 7 2 0 3 1 in 30 48% 54% 65 and older 2 3 1 8 1 7 3 1 in 13 41% 36% Male 4 4 8 6 1 9 9 1 in 23 47% 48% Female 5 2 2 5 2 2 4 1 in 23 53% 52% White 8 0 6 2 3 7 5 1 in 21 89% 84% Nonwhite 4 6 5 1 3 1 in 36 3% 4% Cell 6 5 4 1 2 2 5 1 in 29 53% — Landline 3 1 7 0 1 9 8 1 in 16 47% — Pollsters compensate by giving more weight to respondents from under-represented groups. Here, we’re weighting by age, party registration, gender, likelihood of voting, race, education and region, mainly using data from voting records files compiled by L2, a nonpartisan voter file vendor. But weighting works only if you weight by the right categories and you know what the composition of the electorate will be. In 2016, many pollsters didn’t weight by education and overestimated Hillary Clinton’s standing as a result. Here are other common ways to weight a poll: Our poll under different weighting schemes Our poll result Don’t weight by education, like many polls in 2016 King +3 Don’t weight by party registration, like most public polls King +4 Our estimate King +5 Weight using census data instead of voting records, like most public polls King +6 Just because one candidate leads in all of these different weighting scenarios doesn’t mean much by itself. They don’t represent the full range of possible weighting scenarios, let alone the full range of possible election results.