That is the view of Debra W. Stewart, president of the Council of Graduate Schools (CGS), a body that represents more than 500 universities in North America, who warned of a "fundamental information gap" facing PhD students.

Speaking in Dublin on 13 September at the European Association for International Education's annual conference, Professor Stewart said that a lack of department-level data prevented students from making informed choices about whether to take PhDs.

Ignorance about career prospects also made it difficult for graduate schools to design courses that were attractive to employers, she added.

"We have some global information about PhD graduates, which is really useful for policymakers, but individual programme information is what is needed," she said.

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"We have to find out what graduates' income is in five, 10 or 15 years' time.

"We need to talk to people over the years and get targeted feedback."

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She said that more than half of PhD students would never pursue academic careers (in some fields the figure was 80 per cent). Therefore, employers' opinions about PhD graduates were vital, for without such insights "it is difficult to develop best practice for preparing the talent we need".

Professor Stewart said that a CGS survey involving more than 6,000 people who undertook postgraduate study between 2000 and 2011, and more than 500 US graduate schools, reveals widespread dissatisfaction with the information provided to students and universities.

More than a third of graduates say they did not receive enough information during their studies about the career-income potential of graduate degrees, the study reveals.

Forty per cent of graduate school deans say students qualify without sufficient knowledge of possible career outcomes, and just 10 per cent are happy with the career guidance students receive from non-academics.

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Greater employer involvement and broader preparation for the workplace were required, Professor Stewart said: "Asking faculty...to advise students about a career in industry is not a good thing. How can we tell them to follow a career we have not pursued ourselves?"

Aggregate information about PhD career earnings is collected in the UK but is normally unavailable to prospective students at the departmental or institutional level.

Janet Metcalfe, chair of Vitae, the UK advisory body for researchers, agreed that more information should be available to PhD candidates but warned that data collection would prove difficult.

"Every programme is an individual experience - you don't have a cohort going through the same course each year," she said. "Giving information at a programme level is therefore not very useful."

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Honest advice about students' chances of pursuing academic or other careers was more important, she said. "Most university inductions tell students about the career opportunities for doctoral graduates. They want students to have realistic expectations from the start."

jack.grove@tsleducation.com.