How to Read Polling Data

Whenever you see an article that cites polling data, you should add or subtract the true margin of error and consider how the story would change. For instance, the polling average we calculated above had Trump’s approval rating at 41 percent. The true margin of error on this number, based on the rules-of-thumb above, is about plus or minus 3 points. What if Trump’s approval rating were really 44 percent? Or 38 percent? How much would this change the story? In this case, I’d suggest, it wouldn’t change the story all that much. Trump would still be unusually unpopular for a president-elect.

By contrast, national polling averages during the final week of the campaign had Clinton up by 3 to 4 percentage points. By the rules above, the true margin of error on this number was about plus or minus 6 points. That means Clinton could really have been ahead by 9 to 10 percentage points — or that Trump could have been up by 2 to 3 points.2 The story would be completely different, in other words, based on even modest errors in the polling. But very little of the horse-race coverage that I read conveyed that sense of uncertainty.

Source: Can You Trust Trump’s Approval Rating Polls? | FiveThirtyEight