Sunday 24 August 2014

Does reading make kids more intelligent?


In my view, the most that can be said for reading is that reduces the possibility that you might go outside and break a leg playing sports. Certainly that is a valuable contribution to civilization, but some researchers have made the further claim that reading boosts intelligence. Will the intelligence boosting dream never die? Take one large bright pill, follow a convoluted set of mental exercises and then, wham, arise to the soaring heights of genius, (and eventually fall from grace) as in that heart-rending classic, Flowers for Algernon.

The latest paper on this matter is far more crafty than that.

Stuart J. Ritchie, Timothy C. Bates and Robert Plomin (2014) Does Learning to Read Improve Intelligence? A Longitudinal Multivariate Analysis in Identical Twins From Age 7 to 16. Child Development. 24 JUL 2014 DOI: 10.1111/cdev.12272


The authors eschew get-bright-quick schemes and concentrate on whether humble reading ability precedes later increases in intelligence in identical twins. Their core argument is that if one identical twin reads better than their identical twin brought up in the same household, then the difference is unlikely to be their identical genetics, so more likely to be a specific (not shared) environmental effect of some sort. Whatever it is, if they can show it boosts intelligence, then this would be a proven example of the environmental influence of reading ability (due to teaching techniques perhaps) on intelligence, and a possible pathway to boosting intelligence through education.

Here is their plan: Using a longitudinal monozygotic (MZ) twin differences design, we test whether twins who—for purely environmental reasons—acquire better reading skills than their co-twin show improvements in intelligence, and whether these associations are found across five waves of testing. Such a finding would have implications for educational interventions, and may also provide a partial answer to the important question of why children within a family have very different intelligence test scores, despite sharing factors such as genes, parental education, parental personality, and socioeconomic status (Plomin, 2011; Plomin & Daniels, 1987).

I hope that, so far, all this makes sense, but since the authors are clever monkeys the plot gets thicker, and there are many paths in infinite space to be tracked down before clarity ensues. Here is Fig 3 showing the significant associations:





The finding is that Reading Ability Difference at age 7 is related to IQ Difference at ages 9 and 10, and that Reading Ability Difference at age 10 is related to IQ Difference at age 12 and Reading Ability Difference at age 12 is related to IQ difference at age 16. It certainly looks as if the twin with the better reading goes on to get better intelligence test results a few years later.

Table 1 shows the raw results for the particular tests used. The sample sizes, means and standard deviations for the IQ subtests are shown. These tests were administered individually by telephone, using a booklet mailed to the twins’ home prior to testing
(Petrill, Rempell, Dale, Oliver, & Plomin, 2002). Stuart Ritchie has kindly sent me the distributions for the 7 year olds, and it looks like they did less well on Similarities than the other tests, but this must be seen in the context of their being raw scores, not standardised scores:

All the scores in the descriptive table are raw scores, but when they go into the model, they are controlled for age and sex and standardized (the model has no mean structure, just correlations). The tests used in TEDS are not the exact ones from Wechsler - they’re often based on those tests, but with some extra items added to make them harder for the older age groups. I’m not sure on what basis this was done, but obviously the decision was made at some point that they had to keep scaling up the difficulty rather than using the standard, normed tests.

The problem with this, as hinted above, is that you can’t use any kind of latent growth curve approach (like we do regularly in the Lothian Birth Cohort data) - because the tests aren’t the same at each time point, you can’t compare means. It’s harder to do this with kids of course, who are getting better with age rather than worse. Elliot Tucker-Drob, in his Texas Twin sample, always makes sure that there’s one identical test that overlaps two of the waves, so that there’s something to anchor the growth curve. I’m not actually certain how this works in practice, but in the next few years I suppose his Texas Twins papers will be appearing and we’ll find out...

The authors conclude: The present study provided compelling evidence that improvements in reading ability, themselves caused purely by the non-shared environment, may result in improvements in both verbal and nonverbal cognitive ability, and may thus be a factor increasing cognitive diversity within families (Plomin, 2011). These associations are present at least as early as age 7, and are not—to the extent we were able to test this possibility—driven by differences in reading exposure. Since reading is a potentially remediable ability, these findings have implications for reading instruction: Early remediation of reading problems might not only aid in the growth of literacy, but may also improve more general cognitive abilities that are of critical importance across the life span.

Of course, at the beginning of this essay I may have been a little too harsh in my bleak evaluation of the benefits of reading. This was probably because I did not think that reading increased the power of the intellect. I felt that the size of the cognitive engine remained the same. However, education may act as a gearbox, applying a set of skills to maximise the use of the engine.

In his great poem of AD 835 “A mad poem addressed to my nephews and neices”   Po Chu-I begins with a couplet on this very matter:

The World cheats those who cannot read; I, happily, have mastered script and pen

So, it may be that lack of reading cheats children of (some) intelligence.


  1. Here's the problems, however:

    I'll start with the fundamental weakness of this type of research: "identical" twins are NOT genetically identical, and they certainly aren't phenotypically identical. MZ twin controls can really only be used in a negative sense. If a twin-controlled study failed to find an association between some activity/exposure and some trait, it means the causal relationship doesn't exist. The reverse is not necessarily true, however.

    In this case, would it be at all surprising that the twin with the higher IQ be more apt to read?

    Of course, there's the issue if these observed IQ differences are hollow with respect to g.

    As for this particular study, as I said to Stuart, the differences were frequently not statistically significant. They had to torture the data to make it yield significance in their model. That right there should be a huge red flag.

    I say while this is interesting, it should be treated as a fine oddity. But, as we know, these studies take on a life of their own. It appeals to those who only begrudgingly let go of the blank slate, and have settled on the "half slate" instead. Obviously, something that says you can raise your child's IQ by fostering reading – which is clearly ruled out by the absence of shared environment effects – will be welcomed.

    That, by the way, is another obvious weakness. If nothing in the shared environment – which clearly includes reading, etc – can boost IQ, why would we expect such a behavior to have an unique environment effect? I don't think so.

    1. It appeals to those who only begrudgingly let go of the blank slate, and have settled on the "half slate" instead.

      Only a moron would think the cake could be sliced.

      Black slaters are a straw man of hereditists, all of whom are mentally retarded.

      --- BGI volunteer

  2. Dear Jayman, Yes, what you say is very likely, and I certainly made reference to "infinite paths in space" but I should have taken up your point (had I thought of it) that if the shared environment does not make a difference, then interventions are unlikely to have much general effect. An esteemed person of my acquaintance, to whom I described the study a few minutes ago after lunch, said she doubted that telephone administered tests had as much predictive accuracy as face to face testing, so it may be a case of error variance.

    1. "An esteemed person of my acquaintance, to whom I described the study a few minutes ago after lunch, said she doubted that telephone administered tests had as much predictive accuracy as face to face testing, so it may be a case of error variance."

      That was the other rub, and I almost mentioned it in my comment. In my experience, all these studies claiming to show some (almost always tiny) effect of some environmental intervention on IQ or some other trait seem to be fussing over measurement error. Often compounding error with error.

  3. I glanced at those pictures. It should be known, when someone uses a path analysis, that a strong assumption is needed to valid inferences. It's the equality in stability (reliability) coefficient. According to Rogosa (1980) "A critique of cross-lagged correlation", the variable with strongest stability will have its path coefficient under-estimated compared to the other. When you look at figures 3 & 4 from Ritchie (2014) you'll see the variable reading has a stronger stability coefficient. Then its relative strength is over-estimated somewhat.

    That said, I don't find this study devastating. If you want a neat proof that reading or vocabular skills do not cause IQ, just read "Deafness, Deprivation, and IQ" (Braden 1994). This book is rarely cited by hereditarians. Curious, isn't it ? Among all existing arguments against the cultural-environmental hypotheses, who made the biggest hit ? I will tell you that I'm not sure. But I can tell you I am certain that Braden was among the most devastating. The irony is that he wasn't hereditarian, but just the opposite.

    Briefly, his research concluded as follows. deaf children are environmentally, severally, depressed, have academic achievement lower than the average children, and are severally depressed in their verbal skills, and yet their performance IQ (assessed by reasoning tests) was about 100 points, exactly the same as in the general population. That means neither school deprivation nor verbal deprivation can cause IQ. If they did really cause IQ, and g specifically, you must expect a general impairment. If the effect of such environmental deprivation has a narrow effect, i.e., is dimension-specific, you are certain there is no Spearman effect involved.

    (For the information, I'm writing a review of that book. It surely deserves it. More than everything else.)

  4. Thanks for your post. A researcher has been working on more recent data on deafness and blindness, getting the same results as you mention, but I have always held back from mentioning this because he has yet to publish, and does not want to rile reviewers by pre-publication publicity.

  5. I think there should also be some sort of verbal IQ, non-cumulative, because it seems clear that the verbal IQ is related to the average capacity in qualitative and quantitative terms, to capture and manipulate words to long term.

    The fundamental principle of intelligence in nature is the ability to survival, but we live in complex societies, this connection between the ability to survival and utility abilities were being replaced by super-specialization of functions. Result = we have intelligent people who make and believe in stupid things.

    Perhaps, beyond the ability to capture, recognize and integrate new words, vocabulary, new but invented by others. We use words to communicate or socialize with each other. No wonder that many humanists have higher than verbal IQ, as well as the stereotype Hannibal Lecter makes sense...

  6. The relationship between verbal IQ, education and monetary gains is only the result of its manifestation, just as the result of non-verbal IQ are our, vertically integrated cities.

    Environmental factors are confounded with genetic predispositions, which are not factors, since the term refers to the consequence of a cause.

    While we may use this term combined with this adjective, I see the environmental factors such as interaction between individuals of different levels and I magnitudes which can result in positive or negative consequences.

    Environmental factors as indirect genetic interactions (everything that lives is entirely biological, of course), as the direct genetic interactions, relate to the interaction of the individual with himself, his conscience, while the indirect genetic interactions, relate the awareness of others in relation to the individual under discussion.