I find his COTI quite misleading/confusing. It seems he is counting 100% of health care expenses (100% of premiums) but not counting the ~70-80% of premiums an employer pays the median employee in median weekly earnings.

In the college field, he also uses a semester if college tuition for some reason. Since this is a 1 time cost, it should almost surely be accounted for differently.

In his article he defends all of the choices he made for the COTI calculation. 100% of the premium is used because most people in 1980 paid for the whole thing themselves. I guess it raises the question that the institution of employer sponsorship allowed the costs to balloon, but that is a whole different discussion.