Ritholtz references a research paper that examined 38 states and regions from 1979 to 2016. This research indicated a 7% increase in pay gain, with virtually no change in the overall number of...

Ritholtz references a research paper that
examined 38 states and regions from 1979
to 2016. This research indicated a 7%
increase in pay gain, with virtually no
change in the overall number of low-wage
jobs. What two challenges to the findings of
this research does Ritholtz point out?