Higher education funding heads have admitted that using postcodes to draw up performance targets and allocate cash premiums for widening participation is a blunt instrument.
Maps showing participation rates of students from Wales published by the Higher Education Funding Council for Wales reveal many pockets of low participation in affluent areas, as well as localities with high participation in poorer parts.
Phil Gummett, head of higher education for the HEFCW, said the Welsh funding council shared the data "so that everyone understands the realities behind the broad-brush analysis".
The maps show levels of participation for 2000-01 in Welsh unitary authorities and provide more detailed local-level data.
They show that residents of a ward with a very low participation rate were up to ten times less likely to be in higher education than those in a high-participating ward.
Nearly 45 per cent of the wards considered to have a very low participation level lie in the South Wales Valleys, even though this region accounts for only 19 per cent of all wards. But even here there are pockets of high participation.
Mr Gummett said: "The postcode system is imperfect - it's giving an average account of a picture that everyone recognises is more complex. But thus far it is the least worst instrument we could use."
The Higher Education Funding Council for England, which aims to develop a more sophisticated measure, has yet to publish information for England. Mr Gummett said: "We are interested in the work being done by Hefce and interested to see if what comes out of it is applicable to Wales."