From the Pew Research Center: A basic question when reading a poll: Does it include or exclude nonvoters?

In some 2305 sections we've been discussing polling. Here's an important reminder of what can throw polls off.

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The early days of a new presidential administration produce not just a blizzard of news but a blizzard of numbers. Pollsters of all stripes race to get and report Americans’ first impressions of their new president. But, frustratingly, those reports don’t always match up as precisely as the Type A among us might wish.

Take the past three weeks of polling on President Donald Trump. Depending on the poll, Trump’s approval rating between Feb. 5 and 13 could have been as high as 53% or as low as 39%. So which was it?

There are a number of possible reasons for polls arriving at different estimates – from the mode used to collect data to how people are selected for a survey – but here we’ll tackle one of the most basic: Did the poll include or exclude the 45% of adult Americans who didn’t cast a vote last November?