Saturday, 11 July 2009

Replacing education with psychometrics

Bruce G Charlton

Replacing education with psychometrics: How learning about IQ almost-completely changed my mind about education.

Medical Hypotheses. 2009; 73: 273-277



I myself am a prime example of the way in which ignorance of IQ leads to a distorted understanding of education (and many other matters). I have been writing on the subject of education – especially higher education, science and medical education – for about 20 years, but now believe that many of my earlier ideas were wrong for the simple reason that I did not know about IQ. Since discovering the basic facts about IQ, several of my convictions have undergone a U-turn. Just how radically my ideas were changed has been brought home by two recent books: Real Education by Charles Murray and Spent by Geoffrey Miller. Since IQ and personality are substantially hereditary and rankings (although not absolute levels) are highly stable throughout a persons adult life, this implies that differential educational attainment within a society is mostly determined by heredity and therefore not by differences in educational experience. This implies that education is about selection more than enhancement, and educational qualifications mainly serve to ‘signal’ or quantify a person’s hereditary attributes. So education mostly functions as an extremely slow, inefficient and imprecise form of psychometric testing. It would therefore be easy to construct a modern educational system that was both more efficient and more effective than the current one. I now advocate a substantial reduction in the average amount of formal education and the proportion of the population attending higher education institutions. At the age of about sixteen each person could leave school with a set of knowledge-based examination results demonstrating their level of competence in a core knowledge curriculum; and with usefully precise and valid psychometric measurements of their general intelligence and personality (especially their age ranked degree of Conscientiousness). However, such change would result in a massive down-sizing of the educational system and this is a key underlying reason why IQ has become a taboo subject. Miller suggests that academics at the most expensive, elite, intelligence-screening universities tend to be sceptical of psychometric testing; precisely because they do not want to be undercut by cheaper, faster, more-reliable IQ and personality evaluations.



It was only in early 2007 that I began properly to engage, for the first time in my professional career, with the literature on IQ. Surprisingly, this engagement had been stimulated by a book of economic history. And learning the basic facts about IQ rapidly changed my views on many things, none more so than education.

Just how radically my ideas about education were changed by learning about IQ has been brought home by two recent books: Real Education By Charles Murray [1] and Spent by Geoffrey Miller [2]. In line with analyses of Murray and Miller, I would now repudiate many of my previous opinions on the subject, and advocate a substantial reduction in the average amount of formal education and the proportion of the population attending higher education. In general, I now believe that many years of formal education can and should be substantially (but not entirely!) replaced with ‘psychometric’ measures of intelligence and personality as a basis for evaluating career potential.

In this article I use my own experience as a case study of the potentially-disruptive influence of psychometric knowledge, and discuss further the reasons why basic IQ facts have been so effectively concealed, confused and denied by mainstream elite intellectual opinion in the UK and USA.

The importance of IQ

I have been writing on the subject of education for about 20 years (especially on higher education, science and medical education), but I now believe that much of what I wrote was wrong for the simple reason that I did not know about IQ. Personality traits are important in a similar way to IQ, however personality measurement is currently less reliable and valid than IQ testing, and less-well quantified.

In the early 2000s I argued that modern formal education should be directed primarily at inculcating the ability to think abstractly and systematically [3] and that therefore the structure and not the specific content of education was critical (although ‘science’ – broadly defined – was likely to be the best basis for this type of education [4]). I suggested that higher education should be regarded as a non-vocational process, in which most degrees are modular, and modules were optional and multi-disciplinary, so that each student would assemble their own degree program in a minimally-constrained, ‘pick and mix’ fashion [5]. I also contended that since abstract systemizing cognition was so essential to modernizing societies, a major aim of social reform should be to include as many people as possible in formal education for as long as possible [6].

All of these views I would now regard as mistaken – and the reason is mostly my new understanding of IQ [7], [8], [9] and [10]. Miller concisely explains the basic facts about IQ:

“General intelligence (a.k.a. IQ, general cognitive ability, the g factor) is a way of quantifying intelligence’s variability among people. It is the best-established, most predictive, most heritable mental trait ever discovered in psychology. Whether measured with formal IQ tests or assessed through informal conversations and observations, intelligence predicts objective performance and learning ability across all important life-domains that show reliable individual differences” [2].

The crux of my new understanding is that IQ, and to a lesser but important extent personality traits, are highly predictive of educational attainment. This is a very old finding, and scientifically uncontroversial – but the implications have still not been acknowledged.

Since IQ is very substantially inherited with a true heritability of about 80% [7], [8], [9] and [10] and personality too has about a 50% heritability [11] and [12]; and since both IQ and personality rankings are highly stable throughout a persons adult life [13] (it is, for example, very difficult for educational interventions to have any significant and lasting effect on underlying IQ [1]) – then this implies that differential educational attainment within societies is mostly determined by heredity and therefore not by differences in educational experience.

(The other big factor which influences attainment is of course the large element of chance – which affects individuals unpredictably. However, chance is not completely random, in the sense that many outcomes such as accidental injuries and a range of illnesses are also correlated with IQ and personality [14]).

When full account has been taken of IQ and personality (and the measured effects of IQ and personality have been increased to take account of the inevitable imprecision of IQ measurements and the even greater difficulties of determining personality), and when the presumed effects of chance have also been subtracted – then there is not much variation of outcomes left-over within which educational differences could have an effect. Of course there will be some systemic effect of educational differences, but the effect is likely to be very much smaller than generally assumed, and even the direction of the education effect may be hard to detect when other more powerful factors are operative [1].

I found the fact that differences in educational attainment within a society are mostly due to heredity to be a stunning conclusion, which effectively demolished most of what I believed about education. My understanding of what education was doing was radically reshaped, and my beliefs about the justifiable duration and proper focus of the system of formal education were transformed. I began to realize that the educational system in modern societies was operating under false pretences. It seems that current educational systems are barely ‘fit for purpose’ and (lacking a proper understanding of IQ) are in many instances progressively getting worse rather than better.

In sum, education is more about selection than enhancement, and educational qualifications mostly serve to ‘signal’ or quantify a person’s hereditary attributes [15] – especially IQ and personality. Differential educational experience does not seem to have much of a systemic effect on people’s ability to think or work.

To put it another way – education mostly functions as an extremely slow, inefficient and imprecise form of psychometric testing. And because this fact is poorly understood, those aspects of modern education which are not psychometric are consequently neglected and misdirected.

Policy implications of psychometrics

If psychometric measures of IQ and personality were available, then it would be easy to construct a modern educational system that was both more efficient and more effective than the current one. However, such change would result in a massive down-sizing of the educational system – with substantial and permanent loss of jobs and status for educational professionals of all types including teachers, professors, administrators and managers.

According to Geoffrey Miller’s analysis [2], this impact on educational professionals is likely to be a key underlying reason why IQ has become a taboo subject, and why the basic facts of IQ have been so effectively obfuscated. Miller notes that it is the ultra-elite, most-selective and heavily research-oriented universities which are the focus of IQ resistance. At the same time more functionally-orientated institutions, such as the United States military, have for many decades quietly been using IQ as a tool to assist with selection and training allocations [16].

“Is it an accident that researchers at the most expensive, elite, IQ-screening universities tend to be most sceptical of IQ tests? I think not. Universities offer a costly, slow, unreliable intelligence-indicating product that competes directly with cheap, fast, more-reliable IQ tests. (…) Harvard and Yale sell nicely printed sheets of paper called degrees that cost about $160,000 (…). To obtain the degree, one must demonstrate a decent level of Conscientiousness, emotional stability, and openness in one’s coursework, but above all, one must have the intelligence to get admitted, based on SAT scores and high school grades. Thus the Harvard degree is basically an IQ guarantee”.

“Elite universities do not want to be undercut by competitors. They do not want their expensive IQ-warranties to suffer competition from cheap, fast IQ tests which would commodify the intelligence-display market and drive down costs. Therefore, elite universities have a hypocritical, love-hate relationship with intelligence tests”.

The vulnerability of the elite institutions to IQ knowledge is because most of the assumed advantages of an expensive elite education can be ascribed to their historic ability to select the top stratum of IQ (and also the most desirable personality types): given the stability and predictive power of these traits the elite students are therefore pre-determined to be (on average) highly successful.

Consequently the most elite institutions and their graduates have in the past few decades, both via academic publications and in the mass media, thoroughly obscured the basic and validated facts about IQ. We now have a situation where the high predictive powers of IQ and personality and the stable and hereditary nature of these traits are routinely concealed, confused or (in extremis) explicitly denied by some of the most prestigious and best-educated members of modern society [17].

Four mistaken beliefs resulting from my lack of IQ knowledge

I will summarize under four heading my main pre-IQ errors regarding education.

Mistaken belief number 1: Modern formal education should be directed primarily at inculcating the ability to think abstractly and systematically [3].

Revision: Modern formal education should be directed primarily at inculcating specific knowledge content.

Abstract systematic thinking is exceptionally important in modern societies. And I used to believe that that abstract systematic thinking was mostly a product of formal education – indeed I regarded this as the main function of formal education [3]. But I now recognize that abstract systematic thinking is pretty close to a definition of IQ; and that strongly IQ related (or heavily ‘g-loaded’) educational outcomes – such as differentials in reading comprehension and mathematical ability – are very difficult/impossible to improve in a real and sustained fashion by educational interventions [1].

In other words, a person’s level of ability to think abstractly and systematically is mostly a biological given – and not a consequence of formal education. The implication is that formal education should not be focusing on trying to do what it cannot do – i.e. enhance IQ. Instead, formal education should focus on educational goals where is can make a difference: i.e. the teaching of specific knowledge [1].

Mistaken belief number 2: Structure not content of formal education is crucial [5].

Revision: Content not structure of education is crucial.

I used to think that it did not matter what subject was studied in formal education, so long as the method of education was one which nurtured abstract systematic thinking [3]. I believed that how we learned was more important than what we learned, because I believed that abstract systematic thinking was a result of formal education – and this cognitive ability was more important than any particular body of information which had been memorized.

This line of reasoning meant that I favoured ‘pick and mix’, wide choice and multi-disciplinary curricula as a method of improving motivation by allowing students to study what most interested them, and giving students practice in learning new material and applying systematic thinking in many knowledge domains [5].

The reason that I believed all this has been summarized by Geoffrey Miller:

“The highly selective credential with little relevant content [such as an elite college degree in any subject] often trumps the less-selective credential with very relevant content. Nor are such preferences irrational. General intelligence is such a powerful predictor of job performance that a content-free IQ guarantee can be much more valuable to an employer or graduate school than a set of rote-learned content with no IQ guarantee” [2].

Since IQ is such a powerful influence on educational (and other) outcomes [18], the value of specific educational content is therefore only apparent when IQ has been controlled-for. Since IQ is routinely ignored or denied, the value of educational content is not apparent in outcomes which are sensitive to differences in general intelligence.

Murray argues that variations in the structure and methods of education are not able significantly to influence those educational outcomes which are ‘g-loaded’ such as reading comprehension or mathematic reasoning [1]. Numerous attempts to raise real long-term intelligence (rather than merely raising specific test scores) have failed [19]. However, the subject matter being studied will (obviously!) make a big difference to what gets learned. Once we set aside the delusional goal of enhancing IQ by educational reform, then the subject matter – or curriculum – becomes a more important focus than educational structure and methods.

Charles Murray therefore endorses the approach to ‘Cultural Literacy’ or a core knowledge curriculum pioneered by Ed Hirsch ( This educational philosophy focuses on constructing a comprehensive curriculum of the factual material that people should know, or ‘need to know’. Over the past couple of decades some detailed and well-validated programmes of study have been developed for the USA, and these can be purchased by educational institutions and also home-schooling parents.

It is claimed that such a core knowledge curriculum should enable the student to become a citizen participating at the highest possible social level, and that a shared education in core knowledge should hold society together with a stronger ‘cultural glue’. If such benefits are real, then school, especially between the ages of about 6 and 14, is the best place to follow such a program; since, although the core curriculum involves more than mere memorization, nonetheless memorization is an important element – and young children can memorize information much more easily and lastingly than adults [1].

Understanding IQ has therefore provoked me into a U-turn on the matter of curricula. I now believe that what we learn in formal education is more important than how we learn, because what we learn can have a lasting effect on what we know; while how we learn does not, after all, teach us how to think.

Mistaken belief number 3: A major aim of social reform should be to include as many people as possible in formal education for as long as possible. Ever-more people should get ever-more education for the foreseeable future [6].

Revision: The system of formal education is hugely over-expanded and should be substantially reduced (to considerably less than half its current size). The average person should receive fewer years of formal education, fewer people should attend higher education institutions and do fewer bachelor’s degrees, and those in higher education should – on average – complete the process in fewer years.

The proportion of school leavers entering higher education in the UK has at least trebled over the past three decades, from around 15% to more than 45%. The rationale behind this vast expansion was based on the observation of higher all-round performance among college graduates – better performance in jobs, and also a wide range of other good outcomes including improved health and happiness [6].

However, it turns out that almost all of this differential in behaviours can be explained in terms of selection for (mostly hereditary) intelligence, rather than these improvements being something added to individuals by their educational experience. The main extra information provided by the successful completion of prolonged educational programs (i.e. extra in addition to signalling IQ) is that educational certification provides a broadly-reliable signal of a highly-Conscientious personality.

Miller has neatly described this trait: “Conscientiousness is the Big Five personality trait that includes such characteristics as integrity, reliability, predictability, consistency, and punctuality. It predicts respect for social norms and responsibilities, and the likelihood of fulfilling promises and contracts. A century ago, people would have called it character, principle, honor, or moral fiber. (…) Conscientiousness is lower on average in juveniles, and it matures slowly with age” [2].

Other attributes of a highly-Conscientious personality are self-discipline, perseverance and long-termism [20].

But a person’s degree of Conscientiousness is not a product of their educational experience; rather it is a mostly-inherited psychological attribute which develops throughout life, the relative (or differential) possession of which is stable throughout life [13]. In other words, Conscientiousness is (mostly) an innate ability in a similar sense to intelligence – and similarly difficult to influence by educational means.

It turns out that modern formal education is mainly signalling [15], or providing indirect evidence about, a person’s IQ and personality abilities which they have mostly inherited [1] and [2]. This means that imposing an ever-increasing number of years of formal education for an ever-increasing proportion of the population is ever-increasingly inefficient – and is wasting years of people’s lives, wasting vast amounts of money on the education provision, and imposing huge economic and social ‘opportunity costs’ by forcing people to remain in formal education when their time would often be better spent doing something else (for example something economically-productive or something more personally-fulfilling).

Mistaken belief number 4: Higher education should be regarded as a general, non-vocational process, in which most degrees are modular and multi-disciplinary; and where specialization or vocational preparation should be a relatively brief and ‘last-minute’ training at the end of a long process of education [3], [5] and [6].

Revision: The period of general education should not extend much beyond about 16 (the approximate age of IQ maturity), and this general education should be focused on the basic skills of literacy and numeracy together with a core knowledge curriculum.

At the age of about 16 each person could potentially leave school with a set of knowledge-based examination results demonstrating their level of competence in a core knowledge curriculum; and with usefully precise and valid psychometric measurements of their general intelligence and personality (especially their age ranked degree of Conscientiousness). The combination of psychometric measures of IQ and Conscientiousness would serve the same kind of function as educational evaluations do at present, providing a basis for employment selection or valid predictions to guide the allocation of access to further levels of formal education.

Beyond this I believe that most education should be ‘functional’ or vocational, in the sense of being a relatively-focused training in the knowledge and skills required to do something specific. This functional post-sixteen formal higher education could vary in duration from weeks or months (for semi-skilled jobs) to several years (for access to the starting level of the most highly skilled and knowledge-intensive professions such as architecture, engineering, medicine or law).

But when IQ and personality measurements are available, then the majority of ‘white collar’ jobs – jobs such as management, administration, or school teaching (up to the age of about 16) – would no longer require a college degree. Instead specific knowledge-based training would be provided ‘on the job’, presumably by the traditional mixture of a formally-structured curriculum for imparting the core knowledge and systematic elements with apprenticeship and individual instruction in order to impart specialized skills.

Murray also suggests that much specialist educational certification for careers could in principle be better done by rigorous public examinations such as those for accountancy, than by the medium of minimum-duration college degrees [1].

Measuring personality

The main unsolved problem for this psychometric approach is the evaluation of personality. Most of the current evidence for the predictive and explanatory power of personality comes from self-rating questionnaires, and clearly these would not be suitable for educational and job evaluations since it is facile to learn the responses which would lead to a high rating for Conscientiousness.

Rather than being simply asserted in a questionnaire, a Conscientious, persevering, self-disciplined personality requires to be demonstrated in actual practice. The modern educational system has, inadvertently, evolved in the direction of requiring higher levels of Conscientiousness [20]. The main factor in this evolution has been the progressive lengthening of the educational process (in the UK the modal average age for leaving formal education has increased from 16 to about 21 in the space of 30 years), but educational evaluations have also become less IQ-orientated (less g-loaded) and more dependent upon the ability of students frequently and punctually to complete neat and regular course work assignments [20] and [21].

However, the modern educational system is not explicitly aware that it is measuring Conscientiousness – the changes have been an accidental by-product of other trends, and there was not a deliberate attempt to enhance Conscientiousness-selectivity as a matter of policy. Because the educational system is blind to the consequences of its own actions, there are counter-pressures to make course work easier and more-interesting and to offer more choices – when in fact it would be a more efficient and accurate measure of Conscientiousness to have students complete compulsory, dull and irrelevant tasks which required a great deal of toil and effort!

However, it may be socially-preferable to have students prove their Conscientiousness in the realm of economic employment rather than by setting them pointless and grinding work in a formal educational context. There are plenty of dull and demanding but necessary jobs, the successful and sufficiently-prolonged accomplishment of which could serve as a valid and accurate reliable signal of Conscientiousness. So it would be more useful for people to prove their level of Conscientiousness in the arena of paid work, than by having this measurement task done by formal educational institutions.

An alternative suggestion for evaluating Conscientiousness comes from Geoffrey Miller, who advocates using broad surveys of opinion from families, peers, employers or any reliable and informed person who is in prolonged social contact with the subject [2].


I have previously written about the extraordinary way in which knowledge of IQ in particular, and psychometrics in general, is ‘hidden in plain sight’ in modern culture [17]. The basic facts about IQ are accessible, abundant and convincing for those who take the trouble to look; but modern mainstream intellectual culture has for around half a decade ‘immunized’ most educated people against looking-at or learning about IQ by multiple forms of misinformation and denigration [22] and [23].

The recent books of Murray and Miller marshal more strongly than before the evidence that one major reason for its taboo status is that IQ knowledge has extremely damaging implications for the vast and expanding system of formal education which employs many intellectuals directly, and which provides almost all other intellectuals with the credentials upon which their status and employability depend. Miller’s phrase is worth repeating: “they do not want their expensive IQ-warranties to suffer competition from cheap, fast IQ tests which would commodify the intelligence-display market and drive down costs” [2].

Murray argues that a properly-demanding 4 year, general and core knowledge-based, ‘liberal arts’ degree would be valuable as a pre-specialization education for the high IQ intellectual elite [1]. Perhaps because I am a product of the (now disappeared) traditional English system of early educational specialization, I am unconvinced about the systematic benefits of general education at a college level. I suspect that the most efficient pattern of higher education would be to specialize at age 16 (or earlier for the highest IQ individuals) on completion of the standard core knowledge program; and that liberal arts should mainly be seen as an avocation (done for reasons of personal fulfilment) rather than a vocation (done as a job).

In other words, a liberal arts education beyond core knowledge could, and perhaps should, be optional and provided by the market, rather than being included in the educational ‘system’. For example, in the UK such an education is universally available without any residential requirement at a reasonable price and high quality via the Open University (

But in a system where objective IQ and personality evaluations were available as signals of aptitude, it could be left to ‘the market’ to decide whether the possession of a rigorous 4 year general liberal arts degree opened more doors; or attracted any extra premium of status, salary or conditions compared with a specialized, early vocational degree such as medicine, law, architecture, engineering, or one of the sciences. (There would presumably also be some specialist arts and humanities degrees, mainly vocationally-orientated towards training high-level school and college teachers – as was the traditional English practice until about 40 years ago [3].)

In summary, modern societies are currently vastly over-provided with formal education, and this education has the wrong emphasis. In particular, the job of sorting people by their general aptitude could be done more accurately, cheaply and quickly by using psychometrics to measure IQ and Conscientiousness. This would free-up time and energy for early training in key skills such as reading, writing and mathematics; and to focus on a core knowledge curriculum.

However, for reasons related to self-interest, the intellectual class do not want people to know the basic facts about IQ; and since the intellectual class provide the information upon which the rest of society depends for their understanding – consequently most people do not know the basic facts about IQ. And lacking knowledge of IQ, people are not able to understand the education system and what it actually does.

I can point to myself as a prime example of the way in which ignorance of IQ leads to a distorted understanding of education. Before I knew about the basic facts of IQ, I had articulated what seemed to be a rational and coherent set of beliefs about education. But since discovering the facts about IQ several of my convictions have undergone what amounts to a U-turn.


“A Farewell to Alms: a brief economic history of the world” by Gregory Clark (Princeton University Press: Princeton, NJ, USA, 2007) was the book of economic history which first stimulated my (belated) engagement with the scientific literature of intelligence and personality. The web pages of Steve Sailer have since provided both an invaluable introduction and also a higher education in the subject (e.g.


[1] C. Murray, Real education: four simple truths for bringing America’s schools back to reality, Crown Forum, New York (2008).

[2] G. Miller, Spent: sex, evolution and consumer behaviour, Viking, New York (2009).

[3] B.G. Charlton and P. Andras, Auditing as a tool of public policy – the misuse of quality assurance techniques in the UK university expansion, Eur Polit Sci 2 (2002), pp. 24–35.

[4] B.G. Charlton, Science as a general education: conceptual science should constitute the compulsory core of multi-disciplinary undergraduate degrees, Med Hypotheses 66 (2006), pp. 451–453.

[5] Charlton BG, Andras P. The educational function and implications for teaching of multi-disciplinary modular (MDM) undergraduate degrees. OxCHEPS Occasional Paper No. 12; 2003.

[6] B.G. Charlton and P. Andras, Universities and social progress in modernizing societies: how educational expansion has replaced socialism as an instrument of political reform, CQ (Crit Quart) 47 (2005), pp. 30–39.

[7] N.J. Mackintosh, IQ and human intelligence, Oxford University Press, Oxford (1998).

[8] A.R. Jensen, The g factor: the science of mental ability, Praeger, Westport, CT, USA (1988).

[9] U. Neisser et al., Intelligence: knowns and unknowns, Am Psychol 51 (1996), pp. 77–101.

[10] I.J. Deary, Intelligence: a very short introduction, Oxford University Press, Oxford (2001).

[11] J.R. Harris, The nurture assumption: why children turn out the way they do, Bloomsbury, London (1998).

[12] D. Nettle, Personality: what makes you the way you are, Oxford University Press (2007).

[13] P.T. Costa and R.R. McCrae, Stability and change in personality from adolescence through adulthood. In: C.F. Halverson Jr., G.A. Kohnstamm and R.P. Martin, Editors, The developing structure of temperament and personality from infancy to adulthood, Lawrence Erlbaum Associates, Hillsdale, NJ, USA (1994), pp. 139–150.

[14] G.D. Batty, I.J. Deary and L.S. Gottfredson, Pre-morbid (early life) IQ and later mortality risk: systematic review, Ann Epidemiol 17 (2007), pp. 278–288.

[15] Caplan B. Mixed signals: Why Becker, Cowen, and Kling should reconsider the signaling model of education. . Accessed 06.04.09.

[16] R.J. Herrnstein and C. Murray, The bell curve: intelligence and class structure in American life, Forbes, New York (1994).

[17] B.G. Charlton, Pioneering studies of IQ by G.H. Thomson and J.F. Duff – an example of established knowledge subsequently ‘hidden in plain sight’, Med Hypotheses 71 (2008), pp. 625–628.

[18] L.S. Gottfredson, Implications of cognitive differences for schooling within diverse societies. In: C.L. Frisby and C.R. Reynolds, Editors, Comprehensive handbook of multicultural school psychology, Wiley, New York (2005), pp. 517–554.

[19] Spitz HH. The raising of intelligence: a selected history of attempts to raise retarded intelligence. Hillsdale, NJ, USA: Erlbaum; 1986.

[20] B.G. Charlton, Why are modern scientists so dull? How science selects for perseverance and sociability at the expense of intelligence and creativity, Med Hypotheses 72 (2009), pp. 237–243.

[21] Charlton BG. Sex ratios in the most-selective elite undergraduate US colleges and universities are consistent with the hypothesis that modern educational systems increasingly select for conscientious personality compared with intelligence. Med Hypotheses; in press, doi:10.1016/j.mehy.2009.03.016.

[22] A. Wooldridge, Measuring the mind: education and psychology in England, c.1860–c.1990, Cambridge University Press, Cambridge, UK (1994).

[23] L.S. Gottfredson, Logical fallacies used to dismiss the evidence on intelligence testing. In: R. Phelps, Editor, Correcting fallacies about educational and psychological testing, American Psychological Association, Washington, DC (2009), pp. 11–65.