For the love of all that is good and reasonable, please, everyone, stop using the percentage of scientists becoming research faculty as a measure of PhD oversupply.
If there are too many PhDs, then there will be more scientists than there are faculty positions. This much is true.
But…
This is not the same as saying:
Because programs are producing more PhDs than there are faculty positions, we must have an oversupply problem. This can be false.
Are “we” training too many PhDs? Maybe, maybe not. There is much more to be said on the issue. I just needed to get this out of my system until I find the time to write the rest.
Ever on & on 
I *think* this is sometimes done to compare biosciences to say, humanities, where the faculty market for PhDs is the vast majority of the entire job market where you can actually use your training. There’s little doubt there is an “oversupply” of PhDs broadly, if you think people should get to use their training.
That said, I agree with you for the most part. It’s a bad way to think about things in biosciences, and can serve to further privilege the faculty path. On the other hand, it might be even worse to think about it as “industry will absorb every science PhD we produce, all PhDs get jobs, they all pay 80k+, we are completely immune to market trends, outsourcing can’t happen to R & D, and we need MOAR students” (all things I’ve seen used as operational assumptions).
I think one issue here (which I hope to expand upon soon) is what it means to ‘use your training’, or put another way, what is it we think a PhD in STEM is training for…
If you learned solving PDE’s and are only solving quadratics …. then you are not using your training to its full extent
Looked at from another angle, if we ask why we employ as many postdocs as we do in academic science (whether we “need” these people later for faculty jobs or not), it is hard to avoid the conclusion that it is simply because they are very cheap skilled labor. If academic labs had to pay what industry pays for the same people with the same skills, it would be a serious disruption to the way academic science is done. Likewise if PhD students had to take out massive loans that needed to be paid off, like law or medical students (as it is, phd stipends are the candy that gets you in the van). PIs, institutions, and funding agencies win big in terms of bang for their buck.
And the reason — the only reason — that postdocs will work so cheap is that the vast majority REALLY REALLY want a career that requires this precise work experience and no other. If spending 5 years in industry research instead of an academic postdoc didn’t nullify your chances on the faculty job market, academic labs would have a hard time enticing PhDs with $38,000 and an 80 hour week. Whether during my many years of training I happened to acquire skills (quantitative reasoning, communication skills, project management) that are generalizable to other careers doesn’t really change that fact that it is a system that uses an arbitrary and rigidly defined competitive career path to drive down wages. And yes, calling this “overproduction” will immediately be wrong if we all recognize the general utility of our scientific training and redefine the goals and aspirations that have motivated us for the last 10 years.
Didn’t you get the memo? Doing anything else after getting a PhD other than becoming research faculty is completely useless, a waste of the money spent on your training, and makes you a complete and utter failure worthy of nothing but pity.
The unemployment rate for a PhD in chemistry is 4.6 % (http://cen.acs.org/articles/90/i23/Starting-Salaries.html) . That compares to an unemployment of 4 % for those over 25 years old with at least a BA/BS. For newly minted Ph.D.s in chemistry, the unemployment percentage in 2011 was 9 % according to ACS. In 2011, according to the Labor Department, 9 % was the unemployment percentage amongst those with just a 4 year degree under the age of 25. The numbers at the very least indicate we have enough Ph.D.s in chemistry. I would argue though unemployment percentages should be lower for those with advanced degrees than those with just a BA/BS.
The 4.6 % unemployment number is in contrast to the number for those with an MD, < 1.0 % (http://www.npr.org/blogs/money/2011/01/12/132859364/which-jobs-have-the-highest-and-lowest-unemployment-rates).
I don't have the numbers for a Ph.D. in biochemistry or other biomolecular sciences but I suspect not much better. Alternative careers are great and should be encouraged but do you really need to get a Ph.D. in biochemistry to then work in science policy on climate change (Yes real example)? Lots of ways to learn critical thinking skills. Are we really better off having Ph.D.s in the sciences consulting companies?