What percentage of PhD theses (e.g., physics ones) are rejected nowadays? And why?

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    Probably varies widely by department, location, etc. You shouldn't have to narrow it down, but might you want to? Commented Jan 16, 2014 at 4:43
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    What do you mean by "rejected"? For example, that a thesis defense takes place but the student fails and leaves graduate school without a Ph.D.? What if the student fails but is told to try again later after doing a little more work? What about a student who thinks he/she should graduate but whose thesis committee disagrees and won't schedule a defense? You might be able to find statistics for failed defenses, but by itself that data may not tell you much. (My impression is that most borderline theses never make it to the defense.) Commented Jan 16, 2014 at 8:49
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    At many universities (my experience is exclusively EU-centric) there are at least two self-censorship filters before it comes to a defense. Firstly, and most importantly, it's the thesis supervisor who must approve your manuscript as defensible. Secondly, you often also need a dean's approval for moving on towards an actual defense. There are many theses which do not make it through these safeguard filters on their first attempt, but if the system works, you almost never see an officially failed defense/rejected thesis. Hence the numbers on the actual "failure rate" do not really exist.
    – walkmanyi
    Commented Jan 16, 2014 at 10:20
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    @walkmanyi Same for Austria and Switzerland. I have never heard of somebody 'failing' their defense (that would be an affront against the advisor just as much as against the student), but certainly there are people that just never finish their PhD. I would say, in my group drop-out rate was around 25% - 33%, but I never bothered to count.
    – xLeitix
    Commented Jan 16, 2014 at 13:26
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    In some graduate schools (e.g. the one I'm confronted with at Harvard), one factor is the 'qualifying exam'. I know of someone with a good publication record, whose adviser think she/he perfectly qualifies for the PhD, and who failed her/his qualifying exam. No PhD for that person, although the quality of the work far exceeds the one of the average thesis I have seen in the field.
    – Cape Code
    Commented Feb 12, 2015 at 13:48

2 Answers 2


I'm only personally aware of one student who failed his PhD defense (this is at an R1 US university). After his advisor refused to approve his thesis, he went over his head and got the department chair to schedule the defense anyway. Results were predictable.

On the other hand, "major revisions" are very common, especially, I hear, in the humanities (in engineering, it's far more common to receive token feedback -- if the committee reads the thesis at all! -- than demands for substantial changes).

Outright failing a student during a defense is an extreme embarassment, for the department, for the PhD committee, for the advisor, and of course for the student, so there is every incentive to ensure that a thesis that goes to defense will pass. Moreover, since most theses these days are compilations of previously-published work, it is very easy to tell well in advance if the student is expected to pass.

So if an advisor has doubts about the quality of a student's thesis, he will either ask the student to spend more time improving it, or "suggest" the student start looking for jobs in industry.


Very small, as every failed PhD defence is also a shame for the professor. As a result, the professor will not allow to proceed with defence of the really weak work. And he will listen for other professors that would usually tell in advance they think to vote against.

Hence, most likely, the following will happen:

  • If a PhD student just does not work enough, the professor will not allow to continue studies after some time.
  • If a PhD student is mad with some own theory or topic that academic community unlikely to accept, the professor will not allow to defend such a work.
  • If it is really a bad luck with your topic, the professor will change the topic.
  • If the professor has made a strategic mistake and your diligent work does not give results that could be published in a good journal, the professor should normally try to publish anyway in less reputable sources, good enough for PhD defence.

The PhD supervisor is more interested in your success than a lecturer is interested in the progress of the student. Same professor that writes low grades with relatively little attention (as long as he is sure the student deserves) will spend more time when acting as a PhD supervisor, will try to help, will try to fix the topic. This is because PhD project is also his research project. And who would want ones research project to fail? Of course, the professor tries to find a good PhD student for his project, or, if this was not successful, at least to fire lazy or uncooperative student in the first year. But this is way before the actual PhD defence.

If to ask differently, how many PhD students do not get they degree at the end, this really depends a lot on the traditions inside the institution. However in all places I have seen this was below 20 % or about. The first post doctoral position is also seldom a problem.

The next serious threshold you will need to pass is the professor position or at least a permanent researcher position, if you want to stay in science.

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    Can you provide a link to a university that requires the advisor to approve the thesis before being submitted. In my experience this is not how it works in the US or UK.
    – StrongBad
    Commented Jan 16, 2014 at 14:14
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    Regardless of the rules, it is very uncommon to go to defence against the will of the supervisor, and you really cannot expect to pass if you are in such a conflict, at least in European system. I have seen cases in Germany, Switzerland and Lithuania. Commented Jan 16, 2014 at 14:23
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    To say differently, if the supervisor thinks you will pass, you will most likely pass. And, with the help of your supervisor, it should not be extremely difficult to bring your PhD into good shape. The PhD supervisor is more interested in your success than a lecturer is interested in the progress of the student. But if you are in a conflict instead, chances to succeed are minor. For such a case, I would suggest to change the supervisor instead, even if this would mean changing the university as well. Commented Jan 16, 2014 at 14:52
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    @DanielE.Shub: just a quick example of a university requiring an approval of a thesis supervisor before engaging a panel of examiners/reviewers: TU Delft. See article 18.2 (pg. 24), as well as the formal process description (row 6 in table pg. 8) in the TU Delft doctorate regulations.
    – walkmanyi
    Commented Jan 16, 2014 at 15:26
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    In short. Trust your supervisors. If you have a good relationship with them (or even a bad one honestly), and they think you will pass, then you will almost certainly pass. If: you go over your supervisors head, your supervisors have been sub-par or not supportive, your supervisors have not thoroughly read your thesis, then you have more cause for concern. Commented Jun 19, 2021 at 2:13

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