Posted this on reddit, but I don't think it got "red"
Man. My blog is only ever read by people I know, and I certainly would have been more careful if I'd had any idea this was going to blow up.
Friends have suggested I should clarify some points:
* Nobody suffered permanent marks on their transcript or lost marks from this
* One person lost a bunch of time retaking the course, the others had to go through an ordeal being grilled by me and were then told that I had decided not to follow up.
* I did not enjoy the grilling. Didn't really enjoy any of it after the amazing seating discovery (which may be one of the reasons it took me many years to post).
* It is not at all clear that three or four of these people were innocent: on the occasions where we've observed cheating in person, it has been collaborative.
* I followed up according to my understanding of the McMaster rules. If I find evidence of dishonesty, I'm expected to report it, investigate it, and then report my findings.
The reason the part about grilling them was written cavalierly is that, until now, I've mostly been criticized (though lightly) for letting 7 of the 8 off scot free. Had I expected this to reach a wide audience, I would have written more carefully.
What else? In this test, I think people were broken into big blocks by last name, but were then free to sit where they wanted. The questions were MC questions (often tricky), and I wouldn't expect a large fraction of common wrong answers from people who studied together. It's hard to be sure, though, which is one of the reasons I looked for outliers, instead of using statistics, and then verified with the seating chart. I honestly hadn't thought about the correlation between sitting together and studying together, but if any of the eight people had offered that as a defense, I would have.