Poll of polls: Hagan likely to win re-election
Data from a number of polls suggests U.S. Sen. Kay Hagan will keep her seat once the votes are tallied Tuesday night.
Posted — UpdatedThat said: Democratic Sen. Kay Hagan is poised to win, according to recent polls.
Nevertheless, this situation offers two important lessons.
First, it is better to rely on averages of polls than to put too much stock in any single survey. A lot of polling data has been collected about this race, so we should care more about what, on average, they have found.
Second, sometimes one poll really is inferior. It is important that pollsters are transparent and make their survey instrument available. High Point disclosed their information, and I used it to decide their results were less reliable.
You’ve probably heard someone say that surveys can be made to find anything. That’s an exaggeration, but opinions are influenced by question order and wording, even if there is no intent to manipulate the findings. Among pollsters, it is well known that asking narrow questions about a topic before asking a more general question about it influences the results for the latter. For example, asking about President Obama's handling of the economy before asking about his overall handling of the presidency leads to greater disapproval if most people are unhappy about the economy. On the other hand, first asking about Obama’s overall job approval won't affect later opinions about his handling of specific issues, such as the economy, ISIS or Ebola.
I think High Point, which like WRAL News used SurveyUSA to make the phone calls over nearly identical dates, might have biased their election question. Respondents were asked about the direction of the country and job approval for Obama before being asked about their vote choice. That’s not conventional practice for election polling. In fact, it’s typically seen as bad practice. I am concerned that their question order primed voters to base their voting decision more about Obama than they would otherwise, and doing so increases Tillis' support.
Looking at the polls of polls
All five agree that Hagan leads Tillis, although her estimated lead is incredibly small. The NYT estimate, for example, gives Hagan just a 1.7 percentage point lead, and that’s the largest lead any of these sites have for her. On the low end, Real Clear Politics and Pollster estimate Hagan’s lead is 0.7 percentage point.
Prediction models that take these numbers into account give Hagan a much more comfortable advantage. They estimate Hagan has between a 70 percent and 80 percent chance of winning. While it might seem like her chances of winning are too high given the slim lead in the polls, other data about North Carolina point to her victory. Also, while the lead is small, it is based on tens of thousands of respondents, which is the main virtue of aggregating polling results.
What are some additional signs that Hagan will win?
So, while anything can happen, it looks like Hagan will hold onto her seat. I’ll have more to say about why in subsequent posts when exit-polling data become available. That said, Republicans can take solace that, even in the event Hagan wins, Republicans are just as likely to gain majority control over the U.S. Senate.
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