Dubious Statistics Watch: Thanksgiving Retail Sales

Bloomberg News seems to be running two stories – on the same subject, and by the same authors – at the same time. The first has quite an apocalyptic headline: "U.S. Consumers Spent Average of 3.5% Less on Shopping". Which is scary since we were given to understand that sales would rise by 4% or so over the Thanksgiving weekend. But then comes the second story: "Holiday Sales Increase; U.S. Shoppers Spend Less on Average" – which is just plain weird. Apparently total sales on Black Friday were up by 8.3%, and the 3.5% decline was in sales per person, which wasn't at all clear in the first story.

But what no one quite comes out and says is that the number of people shopping on Black Friday rose by 12.1% this year over last year – which is what would be necessary in order for those two numbers both to be true. The reason they don't come out and say it is that the second story quotes the National Retail Federation as saying that the number of people shopping rose only 4.8% this year.

Clearly, these three numbers are inconsistent with each other: you can't have total sales up 8.3%, sales per person down 3.5%, and total shoppers up 4.8%. It's mathematically impossible. But it's bad form to point out that none of these numbers are particularly reliable, and that at least one of them has to be wrong. Instead, you simply report what you're told, even if it makes your story read like Lewis Carroll.

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