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Social class differences
in IQ: implications for the government’s ‘fair access’ political
agenda
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.
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).
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).
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 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).
***
Table 1: Precise
measurement of Social Class (SC) – Approx proportion of 18 year old
students eligible for admission to three universities of differing
minimum IQ selectivity
Ex-poly - IQ 100
Redbrick - IQ 115
Oxbridge IQ 130
Highest SC– av. IQ
115
84
percent
50
percent
16 percent
Lowest SC– av. IQ
90
25
percent
5
percent
½ percent
Expected SC diff
3.3
fold
10
fold
32 fold
Table 2: Imprecise
measurement of Social Class (SC) – Approx proportion of 18 year old
students eligible for admission to three universities of differing
minimum IQ selectivity
Ex-Poly - IQ
100
Redbrick - IQ
115
Oxbridge - IQ 130
Highest SC –av. IQ
110
75
percent
37
percent
9 percent
Lowest SC –av. IQ
95
37
percent
9
percent
1 percent
Expected SC diff
2
fold
4
fold
9 fold
***
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.
Naturally, this simple
analysis is based on several assumptions, each of which could be
challenged and adjusted; and further factors could be introduced.
However, the take-home-message is simple. When admissions are
assumed to be absolutely meritocratic, social class IQ differences
of plausible magnitude lead to highly significant effects on the
social class ratios of students at university when compared with
the general population.
Furthermore, the social
class differentials inevitably become highly amplified at the most
selective universities such as Oxbridge.
Indeed, it can be
predicted that around half of a random selection of kids whose
parents are among the IQ 130 ‘cognitive elite’ (eg. with both
parents and all grandparents successful in professions requiring
high levels of highly selective education) would probably be
eligible for admission to the most-selective universities or the
most selective professional courses such as medicine, law and
veterinary medicine; but only about one in two hundred of kids from
the lowest social stratum would be eligible for admission on
meritocratic grounds.
In
other words, with a fully-meritocratic admissions policy we should
expect to see a differential in favour of the highest
social classes relative to the lowest social classes at all
universities, and this differential would become very large at a
highly-selective university such as Oxford or Cambridge.
The highly unequal class
distributions seen in elite universities compared to the general
population are unlikely to be due to prejudice or corruption in the
admissions process. On the contrary, the observed pattern is a
natural outcome of meritocracy. Indeed, anything other than very
unequal outcomes would need to be a consequence of non-merit-based
selection methods.
Selected references for
social class and IQ:
Argyle, M. The psychology
of social class. London: Routledge, 1994. (Page 153 contains
tabulated summaries of several studies with social class I IQs
estimated from 115-132 and lowest social classes IQ from
94-97).
C.L. Hart et al. Scottish
Mental Health Survey 1932 linked to the Midspan Studies: a
prospective investigation of childhood intelligence and future
health. Public Health. 2003; 117: 187-195. (Social class 1
IQ 115, Social class V IQ 90; Deprivation
category 1 – IQ 110, deprivation category 7 – IQ 92).
Nettle D. 2003.
Intelligence and class mobility in the British population. British
Journal of Psychology. 94: 551-561. (Estimates approx one standard
deviation between lowest and highest social classes).
Validity of IQ – See Deary
IJ. Intelligence – A very short introduction. Oxford
University Press 2001.
