Many academics remain to be convinced about the value of the professional doctorate, according to a higher education expert.
Growth in the qualifications, which are designed to be relevant to the workplace, is supporting the expansion of doctoral study in Britain and strengthening its research base, according to John Taylor, director of the Centre for Higher Education Management and Policy at the University of Southampton.
But in a paper, "Quality and Standards: The Challenge of the Professional Doctorate", Professor Taylor also highlights concerns about dropout rates. He adds that many academics and some employers still see the PhD as "the gold standard", believing that "any other form of doctorate is, at best, an inferior award and, at worst, jeopardises the whole meaning and understanding of 'a doctorate'."
In the paper in Higher Education in Europe, Professor Taylor examines six professional doctorate programmes. Although he urges caution about drawing clear conclusions from the small-scale study, he found that on five of the courses, a high proportion of students were failing to complete their course.
"The numbers failing to complete are alarming, especially bearing in mind the fees expended by many students, and may even cast doubt over the value of the professional doctorate," his paper says.
Professor Taylor told Times Higher Education that the professional doctorate, which is usually taken part time and often attracts senior professionals, had opened up new approaches to professional development and research.
"We should be looking to develop as many approaches to doctoral study as possible, as long as the quality and standards of a doctorate are maintained. Although I am a strong supporter of it, the traditional PhD doesn't suit everybody," he said.
"People hold very strongly to the standard of the doctorate, so anything that offers a slightly different way of getting to that point is inevitably treated with some suspicion.
"In the wider world, the professional doctorate is beginning to be accepted. Within the academic world - especially within the traditional disciplines - I am not sure that is quite so clear. I think it is a matter of time."
He said the professional doctorate was a "mark of prestige" in some subjects such as engineering, and it was significant that the Quality Assurance Agency, which sets "benchmarks" for academic standards, did not distinguish between the PhD and the professional doctorate.
"Universities need to be rigorous in their application of QAA guidelines," he urged.
Professor Taylor said he thought the key to retention was for universities to be flexible and supportive to professional doctorate students, who were often trying to juggle their studies with a demanding job.
Mark Brundrett, programme director for the doctor of education at Liverpool John Moores University, agreed. "Students are trying to complete a rigorous doctorate at the same time as carrying on with their working life," he said.
Rajani Naidoo, director of studies for the DBA in higher education management at the University of Bath, said: "Our School of Business Management has a high research rating, so we were very clear from the outset that the DBA would be the same standard as the PhD."
Andrew Stephenson, a research leader at the University of East London, said completion rates were not substantially different among students taking PhDs.