Sir: Stephen Pritchard ("Who supervises the supervisors?", 2 March) is incorrect when he writes that the internal examiner for PhD students is usually the supervisor. Most reputable universities recognise that the supervisor cannot be sufficiently disinterested to act as an effective examiner.
The argument that the supervisor is the only possible person expert enough locally to act as examiner is seldom valid - examiners who are not in the immediate field of research often make excellent and very conscientious examiners, requiring the student to express and discuss the work of the thesis clearly and in simple terms. I have found that, not infrequently, this reveals gaps in understanding which, having escaped the supervisor, fully justify significant revision and improvement of the thesis.
J. E. DALE