CAVEATS
We recognize that in using a simple model, several parameters that are not part of our analysis may pose limitations (Ghaffarzadegan et al., 2011). One consideration is that many engineering doctorates are not interested in academic positions and may not even compete for tenure-track positions in academia. Another consideration is that some engineering graduates are foreign citizens who take academic positions outside of the USA.3 Another factor is inter-field hiring. Engineering doctorates might obtain positions in other fields such as science or business, which would also diminish the gap.