Today's 2nd Buggy Topic

No need to add much here by way of introduction: the second prof bug topic today reflects the subject-title above, and you'll find it set out in a thread at Carpe Diem, the impressive data-driven economic blog of Professor Mark Perry of the University of Michigan.  Click here for the link.  And please note an unintended repetition in the lengthy bugged out comment there starting with the end of point (6 

Can't say why.  And maybe Prof Perry will be kind and delete the repeated materials if he has a chance.