Fresh off our success decoding airline flight tables, I promised them we were going to crack the secrets of grocery stores wide open but to do so we'd need a lot of data. If we each sampled three data points, that'd suffice.
I gave them the weekend. I gave them a week's worth of homework credit. I let them work with a partner.
33% of the class submitted data. That's a pity. Even worse is the difference between the data I personally gathered last September (blue diamonds) and the noise my students submitted (pink squares) some of which was almost laughably fabricated. (As in, I laughed when I saw it.)
For perspective, I have one really exceptional outlier out of the thirty-six transactions I recorded: the person who took six minutes to purchase twenty items. It was a disastrous exchange featuring a price check and a ripped register tape. It was so bad that people happily fled that customer's line for longer ones.
Out of my students' thirty-two data points, they observed six transactions that were even more abnormal than that one, including one incredible checker who managed to ring up one hundred items in just eighty-one seconds.
Exactly one hundred items, right?