Reversion to the mean, or: Polling is hard

In today’s edition of Pointlessly Provocative Headlines Based on Fundamental Misunderstandings of How Polling Works, we’ve got this: Support for Trump Plunges 12 Points: Did The Donald Finally Go Too Far?

Did he go too far? Well, sure. The guy is basically modeling (slightly) covert fascism these days. But the entire hook for this story is meaningless, because the supposed decline was just a drop from an outlier in the previous iteration of poll. Reuters/Ipsos had him at 43% a week ago, which was WAY ahead of his national polling average, and way ahead of where this poll has also pegged him recently. So he ‘plunged’ back down to 31%…which is higher than his average on RCP has ever gotten.

What’s more likely? That his support spiked and then collapsed within a few days, or that the previous poll overestimated his support and the newer one simply reverted to the mean?

Look, single polls are tiny data points. You can mostly ignore them. And especially ignore them if they are counterpoised against previous versions of that same poll to try and tell a story of wild swings.

Maybe Trump really is starting to crater. But writing a story like this based on the movement in a single poll is grasping for narrative and a disservice to your readers.

 

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