Check-out Line Maths

posted by Stal on 2009.09.09, under Stal

I have always viewed the check-out lines at grocery stores as a sort of competitive sport. Should I go for a standard line behind 2 full shopping carts? The express line with half a dozen people holding a couple items? The self-check-out line with four potential registers, but which are human-error-prone and likely to result in fail? (Dammit people, stop letting your children sit on the bagging area.) Luckily, the optimal solution to my problem is now at hand. In a study of check-out scanner data from one six-hour shift, Dan Meyer draws some interesting conclusions, noting that check is slower than credit is slower than cash, and the express lane isn’t faster:

You attract more people holding fewer total items, but as the data shows above, when you add one person to the line, you’re adding 48 extra seconds to the line length (that’s “tender time” added to “other time”) without even considering the items in her cart. Meanwhile, an extra item only costs you an extra 2.8 seconds. Therefore, you’d rather add 17 more items to the line than one extra person!

[ dy/dan via MR ]

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