Details were documented by Bruce Charlton (see below). You would have thought that the public policy implications would be of great importance leading to intense public debate. But then, that might make some people feel bad.
Anyway, here's Charlton's answer to the question posed above.
"Typically, the average IQ of the highest occupational Social Class (SC) - mainly professional and senior managerial workers such as professors, doctors and bank managers - is 115 or more when social class is measured precisely, and about 110 when social class is measured less precisely (eg. mixing-in lower status groups such as teachers and middle managers).And here's an excerpt from his paper.
"By comparison, the average IQ of the lowest social class of unskilled workers is about 90 when measured precisely, or about 95 when measured less precisely (eg. mixing-in higher social classes such as foremen and supervisors or jobs requiring some significant formal qualification or training)."
Social class differences in IQ: implications for the government’s ‘fair access’ political agendaSo that was back in 2008. And seven years later, politicians are still not conceding the inevitability of elitism or that the unskilled labouring classes are, on average, not too bright.
Bruce G Charlton
"Since ‘the Laura Spence Affair’ in 2000, the UK government has spent a great deal of time and effort in asserting that universities, especially Oxford and Cambridge, are unfairly excluding people from low social class backgrounds and privileging those from higher social classes. Evidence to support the allegation of systematic unfairness has never been presented, nevertheless the accusation has been used to fuel a populist ‘class war’ agenda.
"Yet in all this debate a simple and vital fact has been missed: higher social classes have a significantly higher average IQ than lower social classes.
"The exact size of the measured IQ difference varies according to the precision of definitions of social class – but in all studies I have seen, the measured social class IQ difference is substantial and of significance and relevance to the issue of university admissions.
The existence of substantial class differences in average IQ seems to be uncontroversial and widely accepted for many decades among those who have studied the scientific literature. And IQ is highly predictive of a wide range of positive outcomes in terms of educational duration and attainment, attained income levels, and social status (see Deary – Intelligence, 2001).
"This means that in a meritocratic university admissions system there will be a greater proportion of higher class students than lower class students admitted to university.
"What is less widely understood is that – on simple mathematical grounds – it is inevitable that the differential between upper and lower classes admitted to university will become greater the more selective is the university.
"There have been numerous studies of IQ according to occupational social class, stretching back over many decades. In the UK, average IQ is 100 and the standard deviation is 15 with a normal distribution curve.
"Social class is not an absolute measure, and the size of differences between social classes in biological variables (such as health or life expectancy) varies according to how socio-economic status is defined (eg. by job, income or education) and also by how precisely defined is the socio-economic status (for example, the number of categories of class, and the exactness of the measurement method – so that years of education or annual salary will generate bigger differentials than cruder measures such as job allocation, postcode deprivation ratings or state versus private education).
"In general, the more precise the definition of social class, the larger will be the measured social class differences in IQ and other biological variables.
"The non-symmetrical distribution of high and low social class around the average of 100 is probably due to the fact that some of the highest IQ people can be found doing unskilled jobs (such as catering or labouring) but the lowest IQ people are very unlikely to be found doing selective-education-type professional jobs (such as medicine, architecture, science or law).
"In round numbers, there are differences of nearly two standard deviations (or 25 IQ points) between the highest and lowest occupational social classes when class is measured precisely; and about one standard deviation (or 15 IQ points) difference when social class (SC) is measured less precisely.
"I will use these measured social class IQ differences of either one or nearly two standard deviations to give upper and lower bounds to estimates of the differential or ratio of upper and lower social classes we would expect to see at universities of varying degrees of selectivity.
"We can assume that there are three types of universities of differing selectivity roughly corresponding to some post-1992 ex-polytechnic universities; some of the pre-1992 Redbrick or Plateglass universities (eg. the less selective members of the Russell Group and 1994 Group), and Oxbridge.
"The ‘ex-poly’ university has a threshold minimum IQ of 100 for admissions (ie. the top half of the age cohort of 18 year olds in the population – given that about half the UK population now attend a higher education institution), the ‘Redbrick’ university has a minimum IQ of 115 (ie. the top 16 percent of the age cohort); while ‘Oxbridge’ is assumed to have a minimum IQ of about 130 (ie. the top 2 percent of the age cohort).
"When social class is measured precisely, it can be seen that the expected Highest SC to Lowest SC differential would probably be expected to increase from about three-fold (when the percentages at university are compared with the proportions in the national population) in relatively unselective universities to more than thirty-fold at highly selective universities.
"When using a more conservative assumption of just one standard deviation in average IQ between upper (IQ 110) and lower (IQ 95) social classes there will be significant differentials between Highest and Lowest social classes, increasing from two-fold at the ‘ex-poly’ through four-fold at the ‘Redbrick’ university to nine-fold at ‘Oxbridge’.
"In other words, according to social class definitions, the average child from the highest social class is from nine-to-thirty times more likely to qualify for admission to a highly selective university than the average child from the lowest social class."