On October 24, NBC-WSJ-Marist released the results of a new poll, in which respondents from Arizona were asked for whom they will vote: Republican Donald Trump or Democrat Hillary Clinton.
NBC-WSJ-Marist poll results
Of those who answered the question, 41.0% said that they plan to vote for former First Lady Hillary Clinton, whereas 46.0% indicated that they would give their vote to real estate developer Donald Trump.
The poll was in the field between October 30 and November 1. The sample size was 719 likely voters. There is a sampling error of +/-3.7 percentage points. Considering this error margin, the race is currently a statistical tie.
Putting the results in context
As any other method, polls are subject to bias. Therefore, as a general rule, you should not have too much confidence in the results of a single poll. Rather than relying on results from single polls, the recommended strategy look at combined polls or, even better, the combined PollyVote forecast that incorporates forecasts from different methods, each of which draws upon different data.
For the following comparison, we translate Clinton's and Trump's raw poll numbers into two-party vote shares. This procedure yields values of 47.1% for Clinton and 52.9% for Trump. In the most recent NBC-WSJ-Marist poll on September 8 Clinton obtained 49.4%, while Trump obtained only 50.6%.
Comparison to other polls
An average of recent polls in Arizona sees Trump at 52.3% of the two-party vote. Compared to his numbers in the NBC-WSJ-Marist poll Trump's poll average is 0.7 percentage points worse. This margin is within the poll's sampling error, which means that the poll is not an outlier.
The poll compared with PollyVote's forecast
The most recent PollyVote predicts Trump to gain 51.9% of the two-party vote in Arizona. That is, Polly's prediction is 1.0 point below his polling numbers. Again, a look at the poll's sampling error suggests that this difference is negligible.