"Rehearsal for the real thing" and "trial run" are phrases frequently used by PhD students and supervisors about mock vivas. But mocks usually bear little resemblance to the real thing, and it is crucial that students realise this. Vivas vary. Like interviews, one can have a pretty good idea of what, in general terms, is likely to happen, but neither the content nor conduct of the viva can be known in advance. Mocks can have an important role in preparing PhD students for the viva, but their value depends on all parties having realistic evaluations of what they can offer.

The more students and supervisors know about mock vivas, and about their purposes and limitations, the greater their potential.

For starters, there isn't just one type of mock viva. The common assumption that a mock is an interrogation of the student about their thesis by the supervisors immediately before the viva ignores the diversity of forms it can take. For instance, one model involves an oral examination on a small section of a student's thesis by a fellow PhD student and an academic, with a peer audience. Alternatively, two academics (not the supervisors) examine them on the whole of their theses in private. There is also the public performance type where academic staff play the parts of "candidate" and "examiners", and the "candidate" is examined on a published article.

The wide range of possibilities becomes clear by identifying the key variables. First, who's examined - student, academic, another PhD student? Second, what text is examined - the whole thesis, part of the thesis, a published article? Third, how many "examiners" are there and who are they - supervisors, other academics, PhD students? Fourth, who is the audience - no one, supervisors, other PhD students, other academics? Finally, when is the mock relative to thesis submission and the actual viva - before or after submission, a week before the actual viva or only one or two days before?

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The only thing that all mock vivas have in common is that they're not rehearsals for the real thing. Accept this, and mocks can serve several different purposes depending on the type chosen. Take, for example, "student-as-candidate" mocks. These can help foster skills useful for the actual viva, such as defending ideas, thinking on one's feet and coping with pressure. Ideally, the "examiners" shouldn't be the student's supervisors. Supervisors may be too familiar and safe for the student, thus reducing the cope-with-pressure element.

Student-as-candidate mocks are useful in that students can gain experience of focusing on and answering different types of questions about the thesis.

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Again, this is particularly the case if the "examiners" are not the supervisors, as supervisors may be too predictable and/or reinforce a particular approach to the work. Skills in managing different types of behaviours and interpersonal dynamics can also be developed. This is particularly so when students are examined on their own work, because then any implied criticisms by the "examiners" are experienced as personal (this is an important feature of the actual viva that encourages some candidates to be overly defensive). Student-as-candidate mocks before submission can provide ideas about refining aspects of the thesis. There is no ideal mock viva. The best package is one that fits the needs of the individual student.

So how can supervisors maximise the benefits of mock vivas? First, identify what you and your student want the particular mock viva to achieve and choose a style accordingly. Second, encourage your students to prepare thoroughly for the mock viva; the process of preparation is important for a constructive experience. Third, ensure that the examiners are well prepared and take the event seriously. Fourth, provide feedback on the candidate's performance - about their ways of answering questions as well as the content of answers. Fifth, and perhaps most important, caution students not to think of a mock viva as a trial run for the real thing. Finally, view mock vivas as one part of a package of viva preparations. Mock vivas have much to offer, but they are no replacement for long-term preparations that should begin soon after the student registers for an MPhil/PhD.

Penny Tinkler is senior lecturer in sociology, Manchester University. Carolyn Jackson is lecturer in educational research, Lancaster University.

They are the authors of The Doctoral Examination Process: A Handbook for Students, Examiners and Supervisors , published by Open University Press, ?19.99.

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