Your IQ in 90 Seconds
The Great Retrodiction: English speakers onlyJames Thompson • May 22, 2019
Science marches on. A researcher writes in to chide me that I have forgotten the fastest intelligence test of all, which masquerades as a simple reading test, but which can reach back 50 years, and in 90 seconds deliver a precise verdict on the best level of ability you had in your prime. Indeed, I hadforgotten this test, despite recently using it in clinical practice. All this comes from Edinburgh, where Jean Brodie was in her prime, and where psychometry is now in its prime.
Picture the scene: the person being tested is handed a page with 50 words printed on it, and asked to read them aloud, one by one. All the examiner has to do is to note whether they have been pronounced correctly. And that’s it. It is called the National Adult Reading Test.
In his email to me the researcher gives estimates of the time taken:
“Three of the testers (between them they have given the NART several thousands of times), asked how long it takes to give the NART, replied: “an average of a minute and a half. Sometimes a minute, and sometimes three”.
This is a quick test, and extremely powerful.
Now a word about Thomas Caxton. Problem is, which word and how to spell it? Having brought his Flemish printing team over to Westminster, Caxton had to decide how to spell the uncouth English language, which was unkempt, various, regional, protean and quite the rising thing. He that the money was to be made by printing in English, and had to decide what English was likely to be understood. Even with Chancery Standard to guide him (craftily, he placed his printing press next door to the national centre (centre) for official document production) he had to made decisions about English. It is said of Caxton that he fixed written English before it had actually “reached a consensus”. I digress, but it is a feature of English that she is not wrote as she is spoke. In this peculiarity lies an informative isotope: children have to learn how to spell, and in doing so learn how they should pronounce what they read.
What dreadful traps lie in wait for those multitudes who have not won the lottery of life by being born British? I and my brothers, despite English schooling, on coming to England had difficulty with idiosyncratic spellings and with the pronunciation of place names. One of us spoke of “Leicester Square” as Lay-ses-ter, not the absurdly correct “Les-ter”. Equally, pronouncing “mortgage” as Mort-gage” not as the approved “mor-gage”. Why was the t silent? Yes, I know is it is a death pledge, as in Morte d’Arthur, and yes, one third of English is French. I blame someone, and Caxton will do.
Perhaps the ability to learn these absurd peculiarities of English is an intelligence test. It is certainly a burden on memory and learning, probably not as onerous as kanji, but a demanding task anyway. If this unremarked school-age skill measures speed and power of learning, then will it fade with age? Why not find out? Take some children who were tested for intelligence aged 11, and test them again in old age. Then, test them on the “reading/pronunciation test”. Then, compare their current and youthful intelligence scores with the estimate derived from the reading test.
If you want just a very quick summary: A short test of pronunciation—the NART—and brief educational information can capture well over half of the variation in IQ scores obtained 66 years earlier. The NART correlates 0.66 with the Moray House intelligence test given at age 11. A 66-year follow-up is a Foxtrot Oscar follow-up.
These are big claims, so if you want a little more detail, here are three relevant papers in support of them:
J. R. CRAWFORD, I. J. DEARY, J. STARR, L. J. WHALLEY. The NART as an index of prior intellectual functioning: a retrospective validity study covering a 66-year interval. Psychological Medicine, 2001, 31, 451–458.
Background. The National Adult Reading Test (NART) is widely used in research and clinical practice as an estimate of pre-morbid or prior ability. However, most of the evidence on the NART’s validity as a measure of prior intellectual ability is based on concurrent administration of the NART and an IQ measure.Method. We followed up 179 individuals who had taken an IQ test (the Moray House Test) at age 11 and administered the NART and the Mini-Mental State Examination (MMSE) at age 77. A subset (Nfl97) were also re-administered the original IQ test.Results. The correlation between NART performance at age 77 and IQ age 11 was high and statistically significant (r= –73; P< .001). This correlation was comparable to the correlation between NART and current IQ, and childhood IQ and current IQ, despite the shared influences on the latter variable pairings. The NART had a significant correlation with the MMSE but this correlation fell to near zero (r= .02) after partialling out the influence of childhood IQ.Discussion. The pattern of results provides strong support for the claim that the NART primarily indexes prior (rather than current) intellectual ability.
The correlation of 0.73 is based on the fact that only the brighter subjects survived the 66 years after taking the test, so there is a restriction of range and when one allows for that, the underlying correlation is 0.78.
The pronunciation test survives even as dementia sets in:
Pronunciation of irregular words is preserved in dementia, validating premorbid IQ estimation
B. McGurn, MB, ChB; J.M. Starr, FRCPEd; J.A. Topfer, BA, MSc; A. Pattie, BSc; M.C. Whiteman, PhD; H.A. Lemmon, MA; L.J. Whalley, MD; and I.J. Deary, PhD
NEUROLOGY 2004; 62:1184–1186
The National Adult Reading Test (NART), used to estimate premorbid mental ability, involves pronunciation of irregular words. The authors demonstrate that, after controlling for age 11 IQ test scores, mean NART scores do not differ in people with and without dementia. The correlation between age 11 IQ and NART scores at about age 80 was similar in the groups with (r=0.63, p < 0.001) and without (r=0.60, p< 0.001) dementia. These findings validate the NART as an estimator of premorbid ability in mild to moderate dementia.
Clearly, intelligence runs through behaviour like carbon through chemistry. Those liable to dementia are those who were lower in intelligence at age 11. Although all the more recent scores are lower in the dementing group, the drop in the NART is explicable by the initial differences in intelligence. Once that is controlled for, it retains its predictive power.
If you did not have any access to a person’s intelligence score at age 11, which in clinical practice accounts for almost all your patients, then you would be guided mostly by the Mini Mental State examination. It is not affected by previous levels, because it is a broad measure of current functioning.
The NART might make you under-estimate the person’s original ability, and the extent to which they had fallen from previous levels. However, the authors say:
If the value of the NART in estimating premorbid intelligence was attenuated in the presence of dementia, then it would be expected that the correlation between NART and MMSE would be different in our two groups. This was not the case.
Predicting and retrodicting intelligence between childhood and old age in the 6-Day Sample of the Scottish Mental Survey 1947. Ian J. Deary, Caroline E. Brett. Intelligence 50 (2015) 1–9
In studies of cognitive ageing it is useful and important to know how stable are the individual differences in cognitive ability from childhood to older age, and also to be able to estimate (retrodict) prior cognitive ability differences from those in older age. Here we contribute to these aims with new data from a follow-up study of the 6-Day Sample of the Scottish Mental Survey of 1947 (original N = 1208). The sample had cognitive, educational, social, and occupational data collected almost annually from age 11 to 27 years. Whereas previous long-term follow-up studies of the Scottish mental surveys are based upon group-administered cognitive tests at a mean age of 11 years, the present sample each had an individually-administered revised Binet test. We traced them for vital status in older age, and some agreed to take several mental tests at age 77 years(N = 131). The National Adult Reading Test at age 77 correlated .72 with the Terman–Merrill revision of the Binet Test at age 11. Adding the Moray House Test No. 12 score from age 11 and educational information took the multiple R to .81 between youth and older age. The equivalent multiple R for fluid general intelligence was .57. When the NART from age 77 was the independent variable (retrodictor) along with educational attainment, the multiple R with the Terman–Merrill IQ at age 11 was .75. No previous studies of the stability of intelligence from childhood to old age, or of the power of the NART to retrodict prior intelligence, have had individually-administered IQ data from youth. About two-thirds, at least, of the variation in verbal ability in old age can be captured by cognitive and educational information from youth. Non-verbal ability is less well predicted. A short test of pronunciation—the NART—and brief educational information can capture well over half of the variation in IQ scores obtained 66 years earlier.
Who bothered to note these minor infractions social behaviour, these shibboleths that ruffle the decorum of the spoken word? It was Hazel Nelson who did this, and her explanations about the development of the test, and how to administer it is given here:
A test which usually takes 90 seconds to administer is capable of reaching back to the abilities of youth, and can estimate pre-morbid intelligence even 66 years later, and even in those citizens in the early stages of dementia. It is used regularly to get estimates of pre-morbid intelligence when patients have had head injuries, or any accidents or illnesses which affect cognitive function.
It may seem a restriction that this test works only for English speakers, a mere 1.5 billion, but as my friend says “one should never look gift horse in the mouth”.
So, should you come across any person who doubts the validity of intelligence testing, grab them by the lapels (if they have no lapels you may skip this step, since there is little point debating with the improperly dressed) and enquire whether there is any branch of social science which, on the basis of a 90 second test, can make such useful predictions.