Social class speaks volumes when it comes to a student's chances of going to college, the sort of degree they study, and how much they earn in their first job.
The most detailed breakdown ever of the socio-economic and geographic background of third-level students paints a disturbing picture of the extent to which postcode determines study and career chances.
The divide is already obvious in Leaving Cert results, with school-leavers from affluent backgrounds most likely to achieve high CAO points, giving them more of a choice of college courses: 32pc of those with 555-600 points were from the wealthiest families, compared with 3pc from the most disadvantaged.
That translates into well-off students - who often have the benefit of smaller classes in fee-paying schools as well as top-up grinds - dominating high-points courses such as medicine, business, finance and engineering, while agricultural, environmental, social work and childcare programmes have higher proportions of students from "disadvantaged" backgrounds.
In one stark example, more than 36pc of enrolments in medicine are from "affluent" families, and only 3.5pc from "disadvantaged" backgrounds.
The advantage enjoyed by the well-off can be gauged from figures showing the 15pc-16pc of the most affluent families represent 19pc of the overall student body.
Another way of looking at it is that 15pc of the second-level school students are defined as "disadvantaged", but only 10pc of higher education students are so classified.
Socio-economic background is also an indicator of likely salary levels after graduation, suggesting postcode and social capital may be a big influence in that first job.
All other factors being equal - in other words, where two graduates have the same degree and the same grades - a student from an affluent family will be paid about 30pc more than one from a disadvantaged background nine months after leaving college.
The breakdown is provided in a new study by the Higher Education Authority (HEA) which for the first time uses the address of individual students and the census's small areas deprivation index to determine socio-economic status. Previously, the HEA relied on students ticking a box for their father's occupation.
The research covers all undergraduate and master's students in 24 publicly funded institutions in 2017/18. It does not include Trinity College Dublin, which had data protection concerns about furnishing students' addresses to the HEA. The matter has been resolved and Trinity will be included in future research, which will be annual.
The report, 'A Spatial and Socio-Economic Profile of Higher Education Institutions in Ireland', provides detailed data on the socio-economic background of students in each college.
University College Cork (UCC), University College Dublin (UCD) and Royal College of Surgeons Ireland (RCSI) have the lowest proportion (5pc) of students from disadvantaged backgrounds.
Generally, universities have much higher concentrations of affluent students than those from disadvantaged backgrounds but, in south Dublin, the Dún Laoghaire Institute of Art, Design and Technology (IADT) has the highest proportion of well-off students, at 35pc.
At the other end of the spectrum Letterkenny IT has the highest proportion of disadvantaged students (24pc).
In the case of most institutions, the socio-economic profiles of their student body reflects the socio-economic make-up of their location.
The findings raise questions about the effectiveness of programmes to level the educational playing field, although the HEA's head of access policy, Caitríona Ryan, said higher education institutions were committed to increasing equity of access and progress was being made.
She said the research provided "a new type of analysis and type of information that we did not have previously, and this will support institutions to develop more targeted approaches to widening access in their regions".
Junior minister for higher education Mary Mitchell O'Connor said improving equality of access to higher education was "a priority" for the Government and the Department of Education.