10

I work in computer science, and am wondering what is the right balance between PhD students and postdoctoral fellows in a lab.

In the previous research group I was, there were one principal investigator professor, one researcher (~ assistant professor), zero post-doctoral fellows, and nine PhD students. In my current research group, there is one principal investigator professor, one post-doctoral fellow, twelve PhD students, and no researchers.

I recently visited a research group in a university where, surprisingly, there are one principal investigator professor, ten post-doctoral fellows and two PhD students.

What do you think is the best ratio between the number of PhD students and the number of post-docs in a research group? Why?

Would you prefer to spend your funding for having more PhD students or more post-docs? Why?

closed as primarily opinion-based by David Z, Peter Jansson, adipro, gman, JeffE Apr 24 '14 at 7:09

Many good questions generate some degree of opinion based on expert experience, but answers to this question will tend to be almost entirely based on opinions, rather than facts, references, or specific expertise. If this question can be reworded to fit the rules in the help center, please edit the question.

  • 3
    Better for what purpose? In what field? – JeffE Apr 22 '14 at 11:08
  • And better for who? – Relaxed Apr 23 '14 at 10:34
  • 1
    Why was the question "put on hold"? Answers involve mainly expertise. – DavideChicco.it Apr 25 '14 at 17:56
2

That's an interesting question. In all of the following, I am assuming computer science here, other fields may have completely different dynamics:

What do you think is the best ratio between the number of PhD students and the number of post-docs in a research group? Why?

PhD students and postdocs fill fundamentally different roles in an university. PhD students are the heart and most important part of a research group. They are where the actual science happens (everybody else is just too busy most of the time). The role of postdocs can vary between "more senior PhD student" to "assistant professor with bad job title", though in most larger research groups it tends to be more the latter than the former. As such, the most common task of postdocs seems to be to take over the day-to-day advising of PhD students from a busy professor. I would say the optimal "formula" for such postdocs is roughly (number of PhD students / 3) - number of professors. The idea being that, as long as the research group is still small, no postdocs are actually needed. In a larger group, you need roughly one postdoc to help about 3 PhD students, minus the few people that the faculty can / wants to actually supervise themselves. In reality, though, the real ratio fluctuates widely based on available funding, people finishing, postdocs moving on, etc.

Let's go over your examples:

one principal investigator professor, one researcher (~ assistant professor), zero post-doctoral fellows, and nine PhD students.

That seems a bit borderline in terms of PhD students per advisor / senior person, but probably still ok.

one principal investigator professor, one post-doctoral fellow, twelve PhD students, and no researchers.

6 PhD students per senior person seems already tough to provide good guidance, especially as the professor certainly will have lots of other things to do as well.

I recently visited a research group in a university where, surprisingly, there are one principal investigator professor, ten post-doctoral fellows and two PhD students.

I guess this is a group where the postdocs are more in the "glorified PhD student" mode. I am not a fan of this model. If the responsible person thinks that 10 postdocs are more productive than 10 PhD students, I think they are sadly mistaken. Or paraphrased from Jorge Cham "as a postdoc you can finally spend all your time on what your PhD training has prepared you to do - applying for faculty positions" (source).

  • 3
    A starting postdoc is more productive than a starting PhD student, because the postdoc has much more experience. The balance evens out toward the end, but there's no doubt that a starting academic wants a few postdocs rather than just PhD students. – aeismail Apr 22 '14 at 8:59
  • @xLeitix Thanks for replying. What do you mean for "glorified PhD student mode"? – DavideChicco.it Apr 22 '14 at 16:43
  • @xLeitix It's not so obvious that having many postdocs and few PhD students is a bad thing, like in the 3rd example. If we can consider postdocs as skilled "almost researchers", and PhD students as "debutante researchers", having many postdocs could be a strong advantage. – DavideChicco.it Apr 22 '14 at 16:46
  • 2
    @DavideChicco.it yes, but they do different things. As a postdoc, a significant amount of time has to go into career development. I might be skilled now, but I sure as heck don't have much time to do actual research. – xLeitix Apr 22 '14 at 21:38
2

Some financial considerations that may have a strong influence on the composition of the research group:

  1. The costs for post-docs and PhD students are different; it is not uncommon to get 2 PhD students for the cost of a post-doc.
  2. Different funding sources may pay for one or the other. For example, I recently got funding that was restricted to PhD students only.

On terms of productivity, I would expect a postdoc to start producing something after 6 months, while PhD students can easily take a couple of years to get something publishable. I would trust a post-doc to co-supervise 1-2 PhD students, but never to be a senior supervisor. You may get a postdoc to be involved in more projects, but then they would not have enough time to progress in their own research.

Not the answer you're looking for? Browse other questions tagged or ask your own question.