In one sense, the subject that authors Paula Stephan and Sharon Levin have tackled here is almost too big for a single book less than 200 pages long, namely how the factors of age, place and time can factor into and affect the careers of scientists in the US. They acknowledge that their data pool is limited to "the physical, earth, and life sciences, with occasional references to mathematics and engineering", in addition to the conclusions being mainly based on US scientists in those areas, rather than looking at scientists all over the world. With those limits, however, the authors do come to some interesting and thought-provoking conclusions, such as these:
a) The major breakthrough contributions by scientists in the top grade (the Nobel Prize-worthy grade, i.e. the "best of the best") do tend to be made by younger scientists, under age 40 or so.
b) However, for average scientists, the quality of their contributions isn't necessarily related to age. In other words, as scientists get older, their quality of research doesn't necessarily decline, perhaps because it was fairly average and not necessarily "outstanding" or "best of the best" to begin with.
c) Being in the right place at the right time ("RPRT", as the authors abbreviate it) is also clearly another factor, much harder to quantify. This really translates into luck, which graduate program and school that a student chooses, if that program and school have professors and research programs that translate into notable careers downstream, in terms of quality of research and the professor's network of colleagues, collaborators and past lab members.
d) In the quarter-century or so prior to publication of this book (1992), the average quality of Americans who have gone into science careers has declined. This is not so much that the top of the top is less stellar, as that the overall pool of people has expanded hugely, so that more people over a wider range of aptitude have entered science. In other words, instead of attracting the top brains and intellects, more people who aren't quite the top tier have gone into science, in the authors' viewpoint.
e) This overall decline in the quality of Americans going into science, as well as challenges in the job market and funding, have made those scientists from that particular quarter-century prior to the book's publication less productive than earlier generations.
f) Because of the increased numbers of Americans in science, the resulting increased competition is actually stifling overall creativity and productivity.
The middle chapters cover the analysis of the historical data that they assembled, and are, for obvious reasons, the heaviest going to try to explain in reasonably clear prose. Even though the authors have tried hard to make this book less of an "academic study, difficult to read" and a book aimed more at policymakers and intelligent lay people, the relative density of the tables, prose and analysis make those middle chapters tougher slogging, to be sure.
In addition, over 20 years after publication, a recent article from the 'Science Careers' section of the 'Science' magazine website by Beryl Lieff Benderly calls into the question the idea, roughly implicit in Stephan and Levin's book, that for the good of scientific productivity, when the time comes for older professors to retire, they should step aside to make way for the younger generation. What Benderly's article covers is the result of something that Stephan and Levin could not have anticipated when they were writing their book, namely the abolition of mandatory university retirement for tenured professors as of January 1, 1994. Benderly, in effect, says that even if all those older professors, including those who aren't that productive, were to retire, replacing them with younger faculty won't necessarily lead to rejuvenation of a university's research program, because, among other reasons:
1. Funding new professors is very expensive, perhaps more so than keeping on established figures.
2. Older professors can still remain productive in old age.
The article is titled "Rethinking the Retirement Bottleneck", and is from the February 5, 2014 issue of 'Science Careers' off their website. (I am not able to paste the link here.)
To their credit, Stephan and Levin do propose some ideas to prevent situations like the glut that currently exists of Ph.D. scientists, although it's questionable that national policy makers have implemented them. For example, the easiest proposal that they mention is a more "sustainable" federal research funding policy of steady increases of 4-5% per year, rather than erratic funding of +15% one year and -2% the next, to use their example. This clearly was not the case in the mid-2000's, where there were sizable increases in funding and a lot of facility construction as a result, only for funding to collapse severly with the downturn in the economy around 2007-2008. Essentially, this was the rough scientific equivalent of the housing bubble. Plus, the current climate of sequestration and an increased presence of the common anti-intellectualism in the US electorate don't help matters at this particular time, in 2014.
While it is rather hard to summarize this book easily (witness the length of this review), it does make for an interesting, if slightly dated, look at the sociological undercurrents to American science in the latter part of the 20th century.