The near tripling of tuition fees may be deterring many more potential students from poor families than official data suggest because of flaws in the way participation is measured, experts have warned.

Statistics on how many young people go on to university from each ward, local authority and region, known as Participation of Local Areas (Polar) data, are the main measure used by the government to track participation in ÖйúAƬ. The latest edition of the dataset, Polar 3, was published earlier this month.

However, teachers' groups and university access experts believe that Polar data paint a misleading picture of the true impact of ?9,000 tuition fees on potential applicants from poor families.

In August, the Independent Commission on Fees, which is sponsored by the Sutton Trust, used Polar data as its main source to conclude that "there has been no relative drop-off in applicants from less advantaged neighbourhoods" - despite observing that 15,000 young applicants to university were "missing" from the system this year.

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That followed an analysis by the Universities and Colleges Admissions Service in July that reported finding no evidence to suggest that high fees had had a "disproportionate effect on (applications from) disadvantaged groups".

Overall, the undergraduate cohort set to begin ÖйúAƬ courses this autumn was about 54,000 smaller than last year's, according to Ucas figures released last month, although university leaders are unsure about the main cause of the shortfall.

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Different stories on the ground

But Graeme Atherton, director of AccessHE, which runs outreach activities in London, said that claims supported by postcode-based data ran contrary to reports from teachers and careers and outreach officers, who had found that poor pupils and those from low-participation areas were less likely to consider university than more affluent teenagers.

"These conclusions appear completely counter-intuitive, and it is not what we're hearing from people on the ground," he said.

Polar's failure to capture pockets of low participation within affluent areas was a major problem, Dr Atherton argued.

A teenager from a low-income family living in a council-flat tower block was wrongly considered to be part of a high-participation group if the family home was in a wealthy postcode, he said.

"Even in London's richest areas, you will have families on low incomes, and they are just not being counted," Dr Atherton said.

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"You only need to have 41 per cent of children going into ÖйúAƬ to be classed as a 'high participation area', so you are immediately not considering 60 per cent of young people.

"Most of London's boroughs are classed as high-participation areas, so if you used this method to target ... resources, you probably wouldn't be working in London at all."

Dr Atherton called for the introduction of a more sophisticated measure, possibly based on actual records of parental income, to assess which teenagers had been put off entering ÖйúAƬ.

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Martin Freedman, head of pay, conditions and pensions at the Association of Teachers and Lecturers, echoed concerns about this "blanket counting method".

"Our members are telling us that children are not so open to university or ÖйúAƬ as a next step," he said. "When you are talking about starting life at 21 with a ?40,000 debt, children are really worried. We need to look at the backgrounds of individual students to see who has not gone on to university."

The calls follow an Ipsos MORI survey of nearly 2,800 state-school pupils conducted last month for the Sutton Trust that found that teenagers from single-parent families were three times more likely to say that their parents could not afford for them to attend university than those from two-parent homes.

However, Seth Fleet, an analyst at the ÖйúAƬ Funding Council for England, thought that Polar data could capture areas of low participation fairly accurately.

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"Young people's participation rates are reported at ward level, a small enough geographical area to highlight real differences in participation rates at a local level," he said.

jack.grove@tsleducation.com.