Becoming a university professor requires a lot of work for very little financial reward, compared to most other professions. In STEM (science, technology, engineering, math) fields, the minimum requirement is four years of undergraduate education, plus anywhere between four and a half and eight years of graduate studies, followed by an (ever increasing) number of years of post-doctoral work. That may get you an assistant professorship where, at a state university, the starting salary is in the $60k-70k range.

(The only other career path I have seen that has similarly low pay for exorbitant requirements is becoming a chef. In both cases, you only do them because you simply love doing them.)

The fortunate few who make it as assistant professors then end up busting their behinds in the hope of getting tenure. A new study published in last week's issue of Science, examined the rates of promotion to tenure at some major US universities. It found that there was no significant difference between the sexes when it came to promotion within an institution. But, in the process, it found that universities aren't doing so well with their investments in young faculty, as only half of their initial hires end up living out their career at the same institution.

Those are sobering statistics for the grad student or post doc, but they should also be sobering for the universities that are employing these professors. Setting up a laboratory or research program does not come cheap. Typical startup costs footed by a university may range from around $110k on the low end to over $1.5MM on the high end, and it can take years for that investment to start producing research.

Tracking research careers

The authors of the Science letter tracked the careers of 2971 faculty members who were hired as assistant professors between 1990 and 2009. Most of the data came from public course catalogs at 14 universities: Boston University, Columbia, Cornell, George Washington University, Georgia Tech, MIT, Northeastern, RPI, University of Delaware, University of Maryland at Baltimore County, University of Massachusetts at Amherst, University of Rhode Island, and Virginia Tech.

Using these sources, the authors figured out the year each individual was hired, (if applicable) the year that they were promoted from assistant professor to associate professor, and (again, if applicable) the year they were promoted from associate to full professor, and finally (once again, if applicable) the year they left academia. They also tracked the sex of the faculty member.

Interestingly enough, both of my alma maters (UD and UMass Amherst) were included in the study. While the faculty's names were withheld, anyone who spent time in the departments could easily pick out some of the professors who were included in the data.

This led me to note a bit of an oddity in how the paper presents its data. The study only tracked individuals who were hired as assistant professors. If they either left the university or left the tenure track, they were considered to have not received tenure (at least as far as the data is presented). Unfortunately, there didn't seem to be a category for people who switched universities part way through their careers.

I was able to positively identify at least one professor (and possibly a second) who switched schools but continued on the tenure track at a different university, a practice that's fairly common in the academic world. Since that person is no longer employed, for the purposes of the study, that individual is counted as no longer being on the academic track where they were hired. So, it gives a decent indication of the payoff a university gets after its investment in startup costs.

What it doesn't capture, however, is the overall rate of success in the field, since some individuals will undoubtedly get tenure at another institution. Unfortunately, the authors simply label their plots as "years in tenure track," which implies they were measuring overall success.

The leaky pipeline on the way to tenure

That issue aside, the study looked into how long a person stayed in a tenure track position at a single institution, and whether there is a gender gap apparent. The gender gap in STEM fields is the product of a "leaky pipeline," where fewer females are present at each step in academia. Previous studies have found that this is not the product of unfair hiring practices; rather, the pool of females looking to go onto the next stage shrinks as you go higher up the academic chain. The relatively few women who do apply for these positions get hired at the same rate as their male counterparts.

A wide variety of STEM disciplines were represented by the nearly 3000 individuals tracked by this study. The data indicate that there is no statistically significant gap between men and women. Of those hired between 1990 and 1993, the average time to become a full professor was 10.73 years for men, and 10.91 years for women. As the authors point out, these results "give a broad view of parity between men and women in the areas of retention and promotion, consistent with several other studies."

But a lot of people of both sexes were dropping out or moving elsewhere. Half of all individuals tracked who were hired by 2001 had left their institution within 10.9 years. Of those hired by 1997, 64.2±3.65 percent were promoted to assistant professor.

These statistics aren't enough to help departments focus on people who may need help to stay on the tenure track (if nothing else, as a way of protecting their investment in startup money). To aid in that task, the study looked at the survival plots for individuals in tenure track positions. They found that large declines in people remaining in academia occurred at years five, eight, and ten; and that post-tenure faculty leave at a lower rate then pre-tenure faculty.

The rate of attrition of faculty members peaks at year six, which makes sense—this was the make-or-break period where one came up for tenure review for the first time. The authors suggest that universities looking to retain their valuable human resources focus additional attention on faculty members late in the pre-tenure period, as this is where they were most likely to leave.

The researchers also looked at whether there were any differences based on academic discipline. People stayed in tenure track positions the longest in mechanical engineering, with the median for men at 16.19 years and median for women at 10.41 years (a wide distribution meant that their 95% Confidence Intervals overlapped, so the difference was not statistically different). The discipline with the shortest time spent on the tenure track was, by far, mathematics. Here, the median time for men to stay in a tenure track position was 7.33 years, and for women a scant 4.45 years. Mathematics also held the distinction of being the only field where there was a statistically significant difference between the retention times for men and women.

The authors conclude that the general lack of gender disparity is good news for departments who want to see their faculty represent the population as a whole. It shows that women, once hired, remain in their position just as long as their male counterparts.

However, as the authors point out, prior work has estimated that it could take 40 years before the gender distribution in a STEM department matches that of the hiring pool, simply because careers can last so long in academia. Extrapolating from current trends and data, the authors conclude by saying that it could be 100 years before women and men each hold half the slots on the faculty of a typical STEM department.

Science, 2012. DOI: 10.1126/science.1214844