NBC-WSJ-Marist published the results of a new poll on July 14. In this poll, interviewees from Pennsylvania were asked for whom they would vote if Hillary Clinton were the Democratic Party's candidate and Donald Trump were the Republican Party's candidate.
NBC-WSJ-Marist poll results
The results show that 45.0% of respondents intend to cast a ballot for former New York Senator Hillary Clinton, whereas 36.0% intend to cast a ballot for real estate developer Donald Trump.
The poll was conducted from July 5 to July 10 among 829 registered voters. Taking into account the poll's error margin of +/-3.4 percentage points, the difference between both candidates is statistically significant.
Putting the results in context
As any other method, polls are subject to bias. Therefore, as a general rule, you should not focus too much on the results of a single poll. Rather than trusting the results from single polls, research in forecasting recommends to consult combined polls or, even better, the combined PollyVote forecast that uses forecasts from different methods, each of which draws upon different data.
For the following analysis, we convert Trump's and Clinton's raw poll numbers into two-party vote shares. This yields figures of 55.6% for Clinton and 44.4% for Trump. On April 27 Clinton received 58.1% in the NBC-WSJ-Marist poll and Trump received only 41.9%.
Results in comparison to other polls
Clinton is currently at 52.0% of the major two-party vote in an average of recent polls in Pennsylvania. Relative to her numbers in the NBC-WSJ-Marist poll Clinton's poll average is 3.7 percentage points worse. This margin is outside the poll's sampling error, which means that the poll is an outlier.
Results compared to the combined PollyVote prediction
The current PollyVote expects Clinton to gain 52.0% of the two-party vote in Pennsylvania. That is, Polly's forecast is 3.6 points below her polling numbers. Again, a look at the poll's error margin reveals that this difference is significant.