During this annual holiday shopping melee, economists project the implications of our spending for the country’s overall economic health in the coming year. That can be like claiming a warm December day proves global warming. What does this have to do with measurement? Quite a bit, actually, because it shows the implications of improper interpretation of outliers in a data set.

In the spirit of the season, when we’re all expected to spend (or charge) large amounts of money for gifts, it can be interesting to see what the newspapers say about that spending. One of the most important days in the retail trade is “Black Friday,” the day after Thanksgiving. That day is “black” because it’s usually so busy that businesses that weren’t making money (in the “red”) finally start making money and go into the “black.” This year, it’s estimated that 5 percent of all holiday shopping will have happened on that day.

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