Wednesday, 29 January 2014

SES and heritability of intelligence


Many thanks to commenter Paige Harden for feeding in more recent, large sample studies on the heritability of intelligence and the influence of socio-economic status. To reiterate, socio-economic status conflates two sources of variance: genetic and environmental. Your status in society is usually a blend of your efforts and the opportunities open to you in a particular culture. It is not a pure measure of random allocation to occupations, nor even of capricious allocation, though in some non-democratic societies the way upwards is blocked for some groups, often for religious or clan reasons. In modern welfare-state open economies social status is much more likely to be affected by intelligence and personality. The one partial exception is that if you yourself have intelligence and diligence then you are likely to be wealthier than average, and can shield your children to some extent from the inevitable effects of regression to the mean. You can cushion their fall for a while, but others will rise above them.

In the papers below I have highlighted the sample sizes and the dates at which the original data were collected, since both are highly relevant to these sorts of investigations.

Childhood Socioeconomic Status Amplifies Genetic Effects on Adult Intelligence
Timothy C. Bates, Gary J. Lewis, and Alexander Weiss (2013)
Studies of intelligence in children reveal significantly higher heritability among groups with high socioeconomic status (SES) than among groups with low SES. These interaction effects, however, have not been examined in adults, when between-families environmental effects are reduced. Using 1,702 adult twins (aged 24–84) for whom intelligence assessment data were available (data collected 2004), we tested for interactions between childhood SES and genetic effects, between-families environmental effects, and unique environmental effects. Higher SES was associated with higher mean intelligence scores. Moreover, the magnitude of genetic influences on intelligence was proportional to SES. By contrast, environmental influences were constant. These results suggest that rather than setting lower and upper bounds on intelligence, genes multiply environmental inputs that support intellectual growth. This mechanism implies that increasing SES may raise average intelligence but also magnifies individual differences in intelligence.

Comment: Notice that these authors report IQ means by SES (fig 2, page 4) which allows readers to understand what is going on. There is a gradual rise in intelligence with social class, but nothing major, though there would be significant impacts on social class representation at IQ 130.

Studies of early childhood tend to exaggerate the apparent effects of home life on intelligence, but measures taken in late adolescence show far less of an influence. Nonetheless, here is a study showing a genetic influence on intelligence by 2 years of age.

Emergence of a Gene x socioeconomic status interaction on infant mental ability between 10 months and 2 years. Tucker-Drob EM, et al. Psychol Sci. 2011 Jan;22(1):125-33. doi: 10.1177/0956797610392926. Epub 2010 Dec 17.

Recent research in behavioral genetics has found evidence for a Gene × Environment interaction on cognitive ability: Individual differences in cognitive ability among children raised in socioeconomically advantaged homes are primarily due to genes, whereas environmental factors are more influential for children from disadvantaged homes. We investigated the developmental origins of this interaction in a sample of 750 pairs of twins measured on the Bayley Short Form test of infant mental ability, once at age 10 months and again at age 2 years. A Gene × Environment interaction was evident on the longitudinal change in mental ability over the study period (2001-2003). At age 10 months, genes accounted for negligible variation in mental ability across all levels of socioeconomic status (SES). However, genetic influences emerged over the course of development, with larger genetic influences emerging for infants raised in higher-SES homes. At age 2 years, genes accounted for nearly 50% of the variation in mental ability of children raised in high-SES homes, but genes continued to account for negligible variation in mental ability of children raised in low-SES homes.


Finally, in middle to upper class 17 year olds Harden, Turkheimer and Loehlin (2007) have done a study on a larger sample of children (839 twin pairs).Behav Genet (2007) 37:273–283 DOI 10.1007/s10519-006-9113-4123
Genotype by Environment Interaction in Adolescents’ Cognitive Aptitude. K. Paige Harden Æ Eric Turkheimer Æ John C. Loehlin

Abstract In a replication of Turkheimer, Haley, Waldron, D’Onofrio, Gottesman II (2003, Socioeconomic status modifies heritability of IQ in young children.
Psychological Science, 14:623-628), we investigate genotype–environment (G · E) interaction in the cognitive aptitude of 839 twin pairs who completed the National Merit Scholastic Qualifying Test in 1962. Shared environmental influences were stronger for adolescents from poorer homes, while genetic influences were stronger for adolescents from more affluent homes. No significant differences were found
between parental income and parental education interaction effects. Results suggest that environmental differences between middle- to upper-class families influence the expression of genetic potential for intelligence, as has previously been suggested by
Bronfenbrenner and Ceci’s model (1994, Nature-nurture reconceptualized in developmental perspective: a bioecological model Psychological Review, 101:568-586

In terms of sample size this is a better reference than his 2003 paper.



Authors should not keep quoting Turkheimer (2003) as the final word on the subject of SES mitigating genetic effects on the of intelligence. Harden, Turkheimer and Loehlin (2007) is the better reference in terms of sample size, though the data collection happened 50 years ago.

To my mind the best study by far in terms of 1) sample size 2) contemporary data collection and 3) age sample (young adults being the “finished product” as far as establishing their own occupations and social status is concerned) is the Bates, Lewis, Weiss (2013) paper.

My thanks to my commenters and email correspondents. Can we try ensuring that authors include the Bates, Lewis and Weiss (2013) paper when they talk about the effect of socio-economic status? Also, can you remind them that SES is not a pure measure of social unfairness, but contains significant elements of intelligence and personality, which are themselves partially under genetic influence?

Tuesday, 28 January 2014

More genes of genius


Various readers have been contributing comments and additional papers on the genetics of intelligence. The general theme is that Prof Rose’s  Times Educational Supplement article did not present a balanced picture, and left out recent relevant work. The full TES article is available in a link given in a comment by Anonymous 27 January 2014 15:44. The same commenter gives a link to a more up to date, much larger sample study by Handscome et al (2012).

Here are some of the points which have come in by email:

“If twin studies are so flawed why do they yield similar results to adoption studies?  Twin and adoption studies are used throughout the life sciences, not just for intelligence; and their results are reasonable throughout.”

“No one thinks any more that genetic effects are limited to the 2% of the genome in coding sequences.   Current Genome Wide Association studies have been limited to additive effects of common SNPs — the focus now is on the vast majority of DNA sequence variation which is rare.  Genome-wide complex trait analysis uses DNA alone in large samples of unrelated subjects, and by this means estimates substantial heritability and underlines that heritability of complex traits and common disorders (nothing specific to intelligence) is due to many genes of small effect that will be difficult to discover and more difficult to replicate.”   

Twin researchers have told me that the numbers of monozygotic to dizygotic twins in the Turkheimer et al. paper are roughly what is always found, so is no problem. The confounding of race and SES is a problem.  However, there has been quite a bit of subsequent work, some of it supporting the hypothesis that heritability is greater in higher SES families. 

Power is a major concern in Genes x Environment studies. 300 pairs of twins has no power to detect reasonable differences in heritability between groups.  The larger more recent studies tend not to replicate the SES finding of the Turkheimer paper. 

As regards epigenetics, readers have pointed out that it is a mechanism for gene expression, and is not limited to parent-offspring transmission, which is what I had been concentrating on.  Some genes get silenced by methylation. The reason why members of an MZ twin pair differ on measures of methylation is that methylation indexes environmental effects.  

Here are some other readings which bring the story up to date:

Five Years of GWAS Discovery. Peter M. Visscher, Matthew A. Brown, Mark I. McCarthy, and Jian Yang. The American Journal of Human Genetics 90, 7–24, January 13, 2012

Childhood intelligence is heritable, highly polygenic and associated with FNBP1L.     B Benyamin et al. (2013), Molecular Psychiatry 1–6.

Monday, 27 January 2014

Genius in the genes

A recent article “Is genius in the genes” Times Educational Supplement, 24 January 2014 by Prof Rose raises three arguments against the view that genetics has a significant effect on intelligence:

1 That although contemporary studies of the genome can account for 40-50% of the variance in intelligence in very large “samples of discovery”, those particular findings account for no more than 3% of the variance when tested on other large samples. That is, they do not replicate well.

2 That one particular paper has shown that heritability of intelligence is high in wealthy families (60%) and low in poor families.

3 That much of the effect on intelligence is not due to genetics but to epi-genetics.

In return, I would like to make three observations:

A) That intelligence is heritable has been shown for over six decades, simply by comparing the high concordance in ability of identical twins with the lower concordance of ability in fraternal twins. Genetic similarity is the most plausible cause of this intellectual similarity. Other techniques, including comparing the intelligence of distantly related persons with those of entirely unrelated persons sustain the view that relatedness in genetics leads to similarity in intellectual power. Geneticists have shown that there is an effect across a wide range of consanguinity, but they are still searching for the next step, in which they show exactly how this comes about. Heritability estimates measure the extent of the genetic effect, genomic studies try to identify genetic causes. “Environmentality” estimates still stand, despite the lack of detailed knowledge as to how family and social effects may influence intelligence (perhaps the number of words spoken by mother to child, and the number of books in the house). Similarly, heritability estimates still stand.

B) Turkheimer et al (2003) Psychol Sci. 2003 Nov;14(6):623-8. Socioeconomic status modifies heritability of IQ in young children.

This paper has been quoted at me many times. No problem with that, but one has to read the paper carefully to see if it merits the particular emphasis which is being placed on it. Here is the abstract:

Scores on the Wechsler Intelligence Scale for Children were analyzed in a sample of 7-year-old twins from the National Collaborative Perinatal Project. A substantial proportion of the twins were raised in families living near or below the poverty level. Biometric analyses were conducted using models allowing for components attributable to the additive effects of genotype, shared environment, and nonshared environment to interact with socioeconomic status (SES) measured as a continuous variable. Results demonstrate that the proportions of IQ variance attributable to genes and environment vary nonlinearly with SES. The models suggest that in impoverished families, 60% of the variance in IQ is accounted for by the shared environment, and the contribution of g enes is close to zero; in affluent families, the result is almost exactly the reverse.

Turkheimer et al. begin by noting a difference between correlational studies of inheritance of intelligence (which suggest strong genetic effects) and mean group difference studies of intelligence which suggest an environmental effect of training programs and adoption. They suggest that this may be due to non-linear effects, namely that bad environments have a bigger effect on intelligence, and that once environments are adequate, no further environmental boost takes place. In his very useful summary of the field Earl Hunt (2010) “Human Intelligence” suggests that the best approach is to always give means and correlations, because both are informative. I would go further back into statistical history, and like A.E. Maxwell (1972) “Basic statistics for medical and social science students” ask for a simple plot of the raw data so that we can judge for ourselves what they look like. Statistics are summaries, after all.

The study was conducted on 319 twin pairs of whom 114 were monozygotic and 205 were dizygotic. That is an extraordinarily high number of identical twins. Monozygotic births are usually 3 per 1000, dizygotic births 33 per thousand, a tenfold difference. Something has boosted the number of monzygotics in the sample.

The twins were classified as 43% White, 54% Black, and 3% “other.” The sample included a high proportion of impoverished families. The median number of years of education of the head of household was between 10 and 11 years. The median occupation was “service worker”; 25% of the household heads received occupational ratings of “laborer” or lower, including 14% with no occupation. The median family income was between $6,000 and $7,000 annually, equivalent to $22,100 in 1997 dollars, the most recent year for which an equivalent scale was available. Twenty-five percent of the families had incomes below the 1973 poverty level for a family of four (U.S. Census Bureau, 2002). Opposite-sex pairs were combined with the same-sex pairs in all analyses.

This is a study which should have shown the average IQ for the above classifications. In that way we would have been given points of reference to compare this paper with others, and to help us understand the later statistical analysis.

In fact, if you look back at the Sandra Scarr adoption studies, her preliminary results at 7 years suggested enormous adoptive family effects but the follow up at age 17 showed reduced effects, and stronger correlations with the abilities of the genetic parents. Usually, all studies show a bigger effect of family life on 7 year olds than 17 year olds, which itself argues against the idea family life is a major crucible of intellect.

So, this is a study which in my view should have given more details about means, standard deviations and correlations, which would have made it easier to link up with previous published work. It was conducted at age 7 which would have maximized the effects of family life. The sample size is relatively small by modern standards of genetic research, though is pretty healthy by the less demanding standards of psychological research. There is an extraordinarily high number of monozygotic births. There is no racial breakdown of results, which is a great pity, because it would add good data on child development for different racial groups in America. If, as seems likely, the Black kids were mostly in the poor category with bad family environments (remember that SES bundles together genetic and environmental variables) and the White kids were in the adequate to good environments, then the finding would be tantamount to saying that at age 7 the effects were thus: Black children were largely influenced by their poor environments, White children largely influenced by their genetics (and their at least adequate environments). If the data have been re-analysed or extended in subsequent publications then the picture might become clearer.

In summary, though the finding makes sense, in that bad environments seem to have (deleterious) effects, and adequate to good environments neutral to slightly positive effects, I think it would be better to get more detail about the sample means and correlations, and the distribution of Black and White scores before according this study the status of having major implications for the heritability of intelligence.

C) Epi-genetics. There are certainly some epigenetic effects in mammals, but it remains to be seen how substantial they are. For example, if such effects were substantial then they would reduce the predictable effects of pure genetic transmission, and should reduce heritability estimates. Particularly, the difference between one egg and two egg twins should be very much reduced by things happening outside the genome. Nonetheless, heritability estimates remain high, particularly in adequate to good environments. Further research may improve our understanding, but it is hard to see how it could become a major source of variance.


I think that genetic studies are making all of the running at the moment. Environmental studies have suggested some environmental mechanisms which might boost intelligence, but they are very far away from finding the underlying “memes”. In some ways, the present difficulty in finding exactly how genes account for much of intelligence is reassuring: avoiding false positives is not usually achieved in psychological research. It is good to see geneticists bringing big samples to bear on the heritability of intelligence, and making sure they publish their attempted replications promptly, showing that they have yet to produce replicable results.

The search continues.

Saturday, 25 January 2014

Van de Vliert replies


I have read your interpretation of my remarks on the climato-economic roots of intelligence and fundamental freedoms with considerable interest. Hopefully, the following responses may sharpen your ideas and insights:

(1) As explained in par. R4.2 on pp.513-514, not all ambient temperature is climate. This is most clearly evidenced by the fact that cold and hot weather cannot have a joint psychophysiological impact at the same time, whereas the combination of cold winters and hot summers does have joint impacts on human functioning (e.g., more suicides, as reported in my 2009 book on pp. 46-51).

(2) Of course, climatic demands do influence national wealth (as exemplified by inhabitants of arctics and deserts), and multiple regression analysis does take this main effect into account when estimating interaction effects of climatic demands and wealth resources on human functioning.

(3) My theory building is a serious attempt to attack too simple explanations of IQ, freedom, etc. in terms of either climate or economy. There is no such thing as myopic determinism! For a succinct treatment of this topic, see Van de Vliert, E., Einarsen, S., & Postmes, T. (2013). Rethinking climatic determinism of conflict. Science published online 16 September 2013:

Hope this helps, with best regards,

Evert Van de Vliert

Friday, 24 January 2014

The climate of intellect


It has been so hot that I have been unable to write anything about an interesting paper on the effects of climate on intelligence.

Climato-economic habitats support patterns of human needs, stresses, and freedoms
Evert Van de Vliert.


The paper runs to 15 pages, and with peer comentary it turns into a 57 page blockbuster, and I have no air-conditioning. The ceiling fans have an ominous tendency to wobble as they gain speed, suggesting that they are about to detach themselves from their fragile moorings, and spin their metal blades through anything they encounter on the way down, an alarming prospect if one is lying naked on the bed beneath. Instead I have been using a floor mounted fan, but that points lovingly at its cousin on the ceiling, and has little effect at bed level. I would attempt to adjust it, but it is too hot to try anything complicated.

It is only thanks to a momentary sea breeze I am able to bring you a brief summary. It appears to be a re-working (or a re-warming) of a familiar hypothesis, that winter sharpens the mind, because without careful planning you might starve before next harvest. Notice: you not only have to survive winter, you have to survive Spring and Summer as well. Not for nothing did the Saxons consider that the end of summer, just before harvest, was a time of great starvation. Failures led to death, and in Elizabethan times it was not unusual for isolated communities to die of famine. Winter keeps people on their toes.

“This core hypothesis is supported with new survey data across 85 countries and 15
Chinese provinces and with a reinterpretative review of results of prior studies comprising 174 countries and the 50 states in the United States. Empirical support covers freedom from want, freedom from fear, freedom of expression and participation, freedom from discrimination, and freedom to develop and realize one’s human potential. Applying the theory to projections of temperature and income for 104 countries by 2112 forecasts that (a) poor populations in Asia, perhaps except Afghans and Pakistanis, will move up the international ladder of freedom, (b) poor populations in Africa will lose, rather than gain, relative levels of freedom unless
climate protection and poverty reduction prevent this from happening, and (c) several rich populations will be challenged to defend current levels of freedom against worsening climato-economic livability.

As you can see, van der Vliert works in Norway, and in that culture people tend to be thorough, though prone to gloom brought on by sunless winters. Theirs is the only economy which is always in surplus, and their sovereign wealth fund makes them all millionaires. Winter has been kind to them, plus oil deposits under the North Sea. However, this is not a paper in the conventional sense, but a summary and overview of many previous studies which have been brought together for this issue. The detailed stuff is in technical appendices.

“Climato-economic theorizing similarly posits that the demands and the resources of the human habitat influence each other’s impact on the needs, stresses, and choices
shared by inhabitants. Greater climatic demands in interaction with poor monetary resources eventually promote avoiding ambiguity by making relatively unfree choices that are necessary and routine rather than autonomous and adventurous. Greater climatic demands in interaction with rich monetary resources eventually promote seeking ambiguity by making relatively free choices that are autonomous and adventurous rather than necessary and routine. This explanation of cultural management of ambiguity and free choice is presented here in subsections describing main effects of climatic demands, interactive effects of monetary resources, differential effects of cold and heat, and shared psychobehavioral adaptations.”

Heady stuff. How good is the argument? First of all, in terms of style the writing is content-rich. It is more than just a winter hypothesis, in that van der Vliert has categorized climates by their level of demand on human behaviour (both cold winters and very hot summers make life difficult, whereas 22 C is the Goldilocks mean) and has also differentiated between rich and poor countries. His focus is very much on human freedoms, which he sees as an outcome of the interplay between climate and resources.



Turning to methods, van der Vliert has put together a measure of climate demand which is more sensitive than simple temperature, and uses that as his climate variable (page 6). Naturally, this is based on modern climate data, whereas in evolutionary terms it would be interesting to estimate climate in earlier times, in so far as this can be done. Monetary resources are calculated in 2004 purchasing power parity dollars. That is OK, but begs the question as to how those countries got to be rich in the first place. The author does not appear to mention national intelligence or scholastic achievement measures, which is a significant omission. However, van der Vliert defends this approach in his reply to the peer commentary, saying that the addition of Lynn and Vanhanen’s IQ by country data did not make much of a difference:

“In a double check, IQ was added to each of the six prediction models in Table R2. In Model 1, national IQ predicted 46% of the variation in overall freedom (b = .04,
n = 71, p < .01), wiping out the initial impact of parasitic disease burden (b = −.11, p = .12). However, Models 2 to 6 then wiped out the initial impact of national IQ,
showing that neither intelligence nor parasitic disease burden mediates the interactive influences of heat demands, cold demands, and monetary resources on
overall freedom. In Model 6, national IQ (b = .01, p =.23), parasitic disease burden (b = .04, p = .55), heat demands (b = −.20, p < .05), cold demands (b = −.09, p
= .51), the interaction of heat and cold demands (b = .02, p = .88), monetary resources (b = .36, p < .01), the interaction of heat demands and monetary resources (b = −.04, p = .76), the interaction of cold demands and monetary resources (b = .50, p < .001), and the three-way interaction (b = −.10, p = .42), accounted for 75% of the variation in freedom from press repression, ingroup discrimination,
and political autocracy. In sum (and in response to Allik & Realo), there is not the slightest indication that Lynn and Vanhanen (2006) were right in assuming that national IQ drives governmental democratization.”

I think that this seems to come down to a battle of the statistical models used, but at least intelligence data are being included, even though conclusions like “not the slightest indication” cast the debate in a dramatic light.

“Accumulating evidence suggests that climatic demands are associated with degrees of fundamental freedom, but that these effects can be observed only if we distinguish
between poor and rich populations. Across studies, climatic demands (M = 5% always accounted for considerably less variation in freedom than both monetary resources (M =27%) and the climato-economic interaction term (M =13%). All in all, repression of freedom is most likely in poorer populations that had to adapt to threatening colderthan-temperate or hotter-than-temperate climates, intermediately
likely in poor or rich populations that had to adapt to comforting temperate climates, and least likely in richer populations that had to adapt to challenging colder-thantemperate or hotter-than-temperate climates. The strength that this conclusion is based on studies addressing different freedoms and using different samples and methods comes with the weakness that the results do not provide independent
evidence. Rather, the results concern slightly different manifestations of overall freedom, loosely patterned around the central themes of threat appraisals, comfort
appraisals, and challenge appraisals (for empirical evidence, see Electronic Supplement 3).

Electronic Supplements 1 through 6 are available at


In sum, this is a different take on the fascinating question of what makes some countries rich and poor, and some tough and other tender: climate.


Monday, 20 January 2014

Fear and loathing in academia


Academic life should be an agreeable pursuit, in which a community of scholars educate their students, and each other. Sometimes it fails to reach that desirable ideal, and becomes a stressful and argumentative trade, creating a poisonous atmosphere from which most recoil but none can really escape.

Why does this happen?

One reason may be that particular sorts of persons are drawn to academic life. The stereotype (which generally contains many of the most noticeable features of any human condition) is that of people who would otherwise be at a loss in ordinary life, too wrapped up in their own interests to attend to mundane matters, other-worldly, not commercially minded, somewhat indifferent to money and outward shows of status, apt to dream up impractical schemes, but generally pretty harmless. It seems more a prescription for a lazy, country club atmosphere than a recipe for conflict. On this evaluation, academics need protection, asylum and institutional support. They are people of the cloister. How on earth can these gentle dreamers ever generate fear and loathing?

One theory lies in their world view, and their politics. Usually, academics incline to the left of the political spectrum, whatever it may be called in the cultures in which they live. The cynical story is that at university everybody makes friends on the basis of sex, drugs and rock and roll, and students are not too bothered about politics till graduation day. Then the right turns to the Right, goes into business and makes money (and pays some taxes) while the left turns to the Left, goes into social service, and works for the government, which is supported by taxes. It is a deal, of sorts. Two very different world pictures find a way of co-existing, to use a communist notion. Even so, following the stereotype, it is the commercial Right who should be tearing each other limb from limb in the savage pursuit of profit, while the Left should cluster together in communal comradeship, toiling together to make the world a better place. Why should community oriented leftists descend into hating?

Perhaps the animus comes when academics identify an odd isolate Rightist who has failed to make the proper career decision, and has remained in academia. In intellectual terms, he is an ugly duckling, and needs to be evicted. It may be as simple as that. Hard to judge, from an historical point of view, whether the Left or the Right have piled up more corpses, but it could be a simple matter of solidarity, or even the tribalism of scholars which makes academics turn on some thinkers of which they disapprove. (On a more general note, if most academics are Left-inclined then this might affect their research results. It would only do so if their methods were weak. Otherwise it should have no effect).

Another theory is that the communitarian world is a sham because outside of a very few scholars with an independent income, academics must fight over a fixed pie of grant money. There is no way to get more other than to beg for more, and that is rarely forthcoming. According to this view the fundamental dependency of academic life is laid bare by the need for publications, grants awards and promotion. One goes into academic for some peaceful thinking, and ends up telling lies on a grant application out of sheer survival. Academics become reduced to prisoners of war fighting each other over scraps of food. It is dog eat dog, all over again. (One way out is to write a successful book which makes money in the real economy. Something like: “How to boost your IQ while dieting”). Absent a source of income, academics will be tempted to denigrate their rivals.

W.S.Sayre, a political scientist at Columbia University is credited with observing: "In any dispute the intensity of feeling is inversely proportional to the value of the issues at stake." By way of corollary, he added: "That is why academic politics are so bitter."

Of course, academics can reply that nature and nurture; the education of children; differences between genetic groups; differences in income and savings; differences in health and lifespan; and different ways to levy taxes and confer benefits are not necessarily low stakes issues, but intensity of feeling often triumphs over the best available findings, and fear and loathing are the result.

Sunday, 12 January 2014

Milometer event 100,001


Returning from dinner at midnight, I decided to check my page view counter, behaviour which constitutes a nervous tick among bloggers. A clear case of operant conditioning. I have got to 100,000 readers. My thanks to all of you.

Pageviews today                              7

Pageviews yesterday                   430

Pageviews last month            14,573

Pageviews all time history   100,001

Entertainingly, the precise midnight result is also a Capicúa or palindrome. Such a number was prized in my youth when it came up on Montevideo bus tickets. I can’t recall getting any, or perhaps they simply didn’t excite me. I learned, very much later, that if you gave them to a girl they were very impressed, and understood that you loved them. Who says mathematics has only a pure, cold beauty and nothing warmer underneath?

Saturday, 11 January 2014

Genes, false positives and sample sizes

It is a simple rule of thumb in psychology that your sample size should be five times larger than the number of variables studied. Indeed, it is a minimal requirement, though one that is often ignored. A ratio of 5 to 1 gives you a chance of finding a signal amongst the noise, but noise will still get the upper hand all too often.

Problem is, this was not always apparent in the early stages of DNA analysis, which provided as many points of comparison as a drunken surveyor stumbling round Stonehenge at the summer solstice. Nearly 700,000 single-nucleotide polymorphisms (SNPs) and 1 million imputed SNPs can be generated by a modern genome wide analysis. Those are big numbers, particularly when your sample size is 2,329 twelve-year-olds for whom DNA and genome-wide genotyping were available. The South London Plomin gang have had to admit defeat in their attempt to name and celebrate the genes for receptive language. That receptive language (vocabulary, semantics, syntax, and pragmatics) at age 12 is  highly heritable is not in doubt. After all, it is a significant component in intelligence, which is also highly heritable. In the current study, the authors attempted to identify some of the genes responsible for the heritability of receptive language ability using a genome-wide association approach. They found that no SNP associations met the demanding criterion of genome-wide significance when they corrected for multiple testing across the genome ( p < 5 × 10 −8). Even the strongest SNP association did not replicate in an additional sample of 2,639 twelve-year-olds.

So, various headlines present themselves: “Receptive language not genetic” seems a clear favourite, with “Geneticists at a loss to explain how we understand language” a close runner. Of course, this overlooks the difference between heritability estimates (which show the extent of the genetic effect without identifying the mechanism) and genomic analysis (which attempts to identify the underlying code).

Of even more interest to science researchers is the following, unremarked, cultural difference. When psychologists publish a finding, they are usually satisfied with describing what they have found in their particular sample. They leave replication to someone else. Geneticists, on the other hand, usually include an attempted replication in the same paper, generally shooting down the original findings “in the sample of discovery”. Perhaps most of psychology is based on false positives derived from over-enthusiastic application of multiple comparisons in “samples of discovery”.

Genome-Wide Association Study of Receptive Language Ability of 12-Year-Olds

Nicole Harlaar; Emma L. Meaburn; Marianna E. Hayiou-Thomas;Oliver S. P. Davis; Sophia Docherty; Ken B. Hanscombe; Claire M. A. Haworth; Thomas S. Price; Maciej Trzaskowski; Philip S. Dale;Robert Plomin

Journal of Speech, Language, and Hearing Research Newly Published on December 23, 2013. doi:10.1044/1092-4388(2013/12-0303)

History: Accepted 22 Apr 2013 , Received 17 Sep 2012 , Revised 18 Feb 2013

The authors conclude that individual differences in receptive language ability in the general population do not reflect common genetic variants that account for more than 3% of the phenotypic variance. (The multiple comparison criterion). They admit that the search for genetic variants associated with language skill will require larger samples and additional methods to identify and functionally characterize the full spectrum of risk variants.

By now you will know my own opinion, which is that psychological research would benefit from collaborative projects which boost representativeness, increase sample size considerably, and utilize a core set of agreed psychological measures. The chance of that happening when the promotion system favours the number of publications is very low: as low as the chance of reliably finding the genes for something in a small sample.

Wednesday, 8 January 2014

Is the dark side of parenting genetic?


In a novel finding, Robert Plomin and colleagues suggest that negative aspects of parenting are more heritable than positive aspects. They call this The Dark Side of parenting. The effect is interesting and subtle: it suggests that whilst parents are generally consistent in their handling of their children, some genetically driven characteristics of their children lead them into more negative parenting styles.

Genetics of Parenting: The Power of the Dark Side
Bonamy R. Oliver, Maciej Trzaskowski, and Robert Plomin
Online First Publication, Developmental Psychology, December 23, 2013. doi: 10.1037/a0035388

They argue that the “dark” side of genetically driven child characteristics plays a bigger role in eliciting parental negativity than do other child characteristics in
eliciting positivity across feelings and control. For example, parental negativity encompassing hostility and harsh parenting may be more responsive to genetically driven challenging child temperament than positive features such as warmth and calmness are to less challenging traits. In simple terms, even peaceable parents get irritable with difficult children.

Theoretical and empirical perspectives on parenting have remained largely founded in Baumrind’s earlier work on parenting styles, which at its core, focused attention on two key aspects of parenting—responsiveness/warmth and demandingness/
control (Baumrind, 1973). While researchers have distinguished aspects of parenting further, most notably in the area of parental control (e.g., Barber & Harmon, 2002) and have varied in their construct labels, these two broad dimensions have been endorsed through numerous studies that have sought to characterize them
Here, we have conceptualized these parenting dimensions as parental feelings (warmth, closeness, hostility, frustration) and parental control (discipline strategies
such as remaining firm and the use of physical discipline); these dimensions have shown robust modest to moderate associations to children’s outcomes (e.g., Parke & Buriel, 2006).

Reviews of behavioral genetic studies have noted that control aspects of parenting tend to yield low estimates of heritability while parental feelings yield moderate estimates (Kendler & Baker, 2007; Plomin, 1994; Rowe, 1981, 1983). To be clear, in
child-based studies, these findings suggest that genetically influenced child characteristics may be more important for eliciting parental feelings than control. However, research has seldom distinguished between positive and negative parental feelings and particularly between positive and negative control strategies. Blurring
the positive and negative sides of feelings and control may mask important underlying foundations of parenting. Harsh discipline and effective supervision, for example, may not be opposite ends of a single continuum, and neither may hostility and warmth. Thus, we hypothesized that the underlying genetic architecture of these aspects of parenting may also be distinct. Specifically, following existing relevant family research  as well as work outside the field we predicted that negativity would show greater heritability than positivity across parental feelings and control as well as within parental feelings and within control.

The sampling frame for the current study was the Twins Early Development Study (TEDS), a population-based, longitudinal study of twins born in England and Wales in 1994–1996, recruited from U.K. birth records. Participants are somewhat better educated than average, but are otherwise representative of the UK.

The current study included 2,260 twin pairs at age 9 (1,202 MZ and 1,058 DZ; 1,034
boys and 1,226 girls), 3,850 twin pairs at age 12 (2,027 MZ and 1,823 DZ; 1,752 boys and 2,098 girls), and 2,293 twin pairs at age 14 (1,231 MZ and 1,062 DZ; 1,028 boys and 1,265 girls).

We generated eight scales from identical parent-report measures at child ages 9, 12, and 14 years of parental feelings and control. For feelings, we used an adapted short form (seven items) of the Parental Feelings Questionnaire (PFQ; Deater-Deckard, 2000) and for control, a short (four-item) discipline (parenting strategies questionnaire adapted from Deater-Deckard, Dodge, Bates, and Pettit (1998). Two
standard composite measures were created at each age from the PFQ and Discipline questionnaires: Feelings from seven PFQ items, including the three positive (e.g., “I feel close to my child”) and four negative items (e.g., “I feel frustrated by my child”) and Control comprising four discipline items including two positive (e.g., “I am firm and calm with him or her”) and two negative (e.g., “I tell him or her off or shout at him or her”) items.

Although face validity for our scales is reasonable and appropriate for the hypothesis-driven nature of the current report, variable internal consistency for these scales was found, with reliabilities lower for scales with fewer items, as is to be expected.

We found across constructs that negative aspects of parenting are significantly more
heritable than positive aspects, again at all three ages. For example, for negative and positive feelings, negative feelings showed significantly more heritability than positive feelings, with average heritabilities across the three ages of 44% and 26%, respectively; the pattern was similar for parental control, with average heritabilities
across the three ages of 27% and 6% for negative and positive aspects, respectively. Finally, creating scales for all the negativity items and all the positivity items regardless of whether they were on the Feeling or Control scale yielded significantly
greater heritability for the negativity than for the positivity, with average heritabilities across the three ages of 44% and 12%, respectively.

For both feelings and control, negativity consistently yielded significantly higher heritability estimates than did positivity, a finding that held for the overall negativity and positivity latent factors (h2  .42 and .10, respectively).

We argue that the “dark” side of genetically driven child characteristics plays a bigger role in eliciting parental negativity than do other child characteristics in eliciting positivity across feelings and control. For example, parental negativity encompassing hostility and harsh parenting may be more responsive to genetically driven challenging child temperament than positive features such as warmth and calmness areto less challenging traits. Distinctions of parenting valence seem to be important for understanding family processes.

One caveat is critical here. In categorizing measures of parenting into positive versus negative valence, we do not include maltreatment. That is, the pattern we report includes aspects of harsh discipline, such as yelling and spanking, but not abusive
forms of parenting. In one study that explicitly looked at this distinction, Jaffee et al. (2004) found that while harsh discipline was moderately genetically influenced (25%), physical maltreatment was not (7%). These findings suggest that children’s genetic influences are largely irrelevant for their vulnerability to maltreatment
and that characteristics of the perpetrator are what are important.

So, one might summarise the findings as saying that when parents deviate into yelling and spanking, it is the genetic characteristics of their children which cause them to do so.

Tuesday, 7 January 2014

Uruguayan cannabis: an export opportunity?


A kind school friend (with whom I did not smoke dope, mostly because she and I were 10 years old at the time) has sent me a newspaper article from El Pais about the interest engendered by the Uruguayan cannabis experiment. As readers of this blog will know, nothing, but absolutely nothing, not even the desperate desire for instant gratification, speeds up the slow process of the local legislative and bureaucratic deliberations. It will be another four months of deep deliberation, assisted by copious quantities of whisky before the weed is made available, at a cost of 0.7 Euros per gram. That is precisely the same as  the current black market street cost. No fools, these legislators. They know they are taking a gamble, but since all other countries have failed to reduce actual cannabis use, they may be on to a winner. They assume that the consumers will prefer a quality assured product, and that the income stream to criminal gangs will be reduced. Perhaps.

However, in an unexpected twist, a new stream of dope heads has opened up: governments. Canada, Israel and Chile have been in talks with local officials about buying large quantities of weed for their own, entirely legal, approved users of medicinal cannabis, as part of pain control for chronic conditions.There is talk of vast laboratories, and government cannabis farms.

So, to the export benefits of beef, lamb, rice, soya bean, tourism and football players, we will shortly be able to add La Droga Uruguaya.  All of this can only happen once the laws are finally passed. But the legislators are on holiday. Drinking whisky.

Hope, fear and Islamic terrorism in America




A very loyal reader wonders if the apparent rise in hope and fear in the last decade is really linked to terrorism, noting that no such rise was apparent for the American Civil War, and the First and Second World Wars. Of course, History is not an experimental science. There is always, as Popper observed, a poverty surrounding historicism. Most grand histories are a collection of “just so” stories. I suppose, tentatively, that the impact of the Twin Towers as a historical event was due to the prospect of a vast global religious war, coupled with the far greater impact of modern television coverage: immediate, lurid, all-consuming. Would previous wars have continued for so long with vivid coverage? cf Vietnam.

Nonetheless, there is a sharp rise in hope and fear after 9/11, in synchrony with a sharp rise in terrorism and as part of a rise in Islamic and even a slight rise in Christianity. There is some evidence of concern and distress at a new source of hatred, from which Americans had been sheltered for most of their history. The Saudi attacks were a vivid shock, plunging the American public into horrible lessons in history and geography.

Vast historical texts have been written on such synchronies. Here, we take a more sceptical approach. Slightly different words and other phrases might paint a differnt picture.  For once I will not be asking for more measures, and for larger sample sizes. No replications please.

Monday, 6 January 2014

After 2 centuries, hope and fear get mentioned again




The clue was in the date. A subtle effect of 9/11. The IRA got the same effect by bombing the Royal Exchange, London, (partly backed by US citizen contributions). Bomb people in Northern Ireland or the Middle East and most readers turn the page. Destroy a big building in a city and governments and citizens pay attention.

Sunday, 5 January 2014

Does education always disappoint?

Continuing my quest for good quality, legal, state sponsored and regulated marihuana in Uruguay, I have been gently enquiring whether people have been signing up at the local pharmacy. So far, no one has admitted to doing so. Instead, they gripe that Uruguay is getting known for the wrong reasons.

However, the main lament, said with great passion, is that the education system is broken. The after dinner talk is that children’s vocabularies have shrunk to the basics required for crude communication. I thought it apposite to compare Uruguay with Spain and Italy, from whence most of its citizens originally emigrated. In fact, both those Iberian nations are within measurement error of each other, but both are better than Uruguay.

              Maths     Reading   Science

Italy         485          490         494

Spain       484           488         496

Uruguay 409           411          416


In terms of trends, Spain has improved by about 2 points since the last assessment, while Uruguay has lost 1 point in Maths, and 2 in Reading and Science. Uruguay has lots of low achievers in Maths, at twice the OECD average. Something is going wrong in maths teaching. Perhaps the locals are right: an education system which was once respected and even admired has lost its way. 6 million dollars is being spent from tight educational budgets just on security to stop school windows being broken by stone throwers. Respect for teachers is waning. It is a little early to blame the Left leaning government (though many do so) and it could be due to: social media, mobile phones, over-generous social security payments, and a lapse of family and Burgher aspirations. It might even be due to free enterprise marihuana, the state sponsored version being yet to hit the streets.

It is little comfort, but Brazil and Argentina are a worse. Come to think of it, it is a great comfort. Uruguay is ahead of its large, overbearing and dysgenically dull neighbours. Scrap all the above.

Friday, 3 January 2014

Shrinking humane genome?

“The fact that the human genome is so parsimonious raises an interesting question. What exactly is it about the human genome that gives rise to our staggering complexity, in the brain for example, compared to other animals such as monkeys, worms or even water fleas?”

Ref: : The Shrinking Human Protein Coding Complement: Are There Fewer Than 20,000

Some alarm is being raised by the finding that our genome appears to be smaller than other lowly and less complex organisms. This is a key result from a new attempt to define what constitutes a gene, in terms of whether it encodes detectable proteins, and whether it is similar to genes in other species.

I feel less affronted. Genes have different histories. Some are very cluttered messy codes, others have done well with sparse and elegant solutions. Anyway, perhaps we are reading the wrong end of the Mandelbrot set, and getting confused by the apparent need to match the end product perfectly with the design code.

However, it suggests an interesting possibility: perhaps humans got fast-tracked by some very favourable set of circumstances. Bipedalism? Fortuitous encephalisation? Eating lots of carrion? Getting friendly with the Neanderthals? Flukes happen.

For the New Year: Living in hope and fear


You and I know that the end of a year is a milometer event, the mere completion of one solar orbit, the defining point set somewhere in mid-winter in Europe, but at other points elsewhere. It is no achievement on our part, though something of an achievement to have worked out that the solar year repeats itself, and a further achievement to have worked out why in terms of Newtonian physics.

Nonetheless, this is a time for hoping that the next year will be better, suggesting that for some mysterious reason the last year had established some sort of aura or depressive groove which can be reset by the magical change of number. At least the Chinese have a better cover story, naming their years so as to allow citizens to ascribe characteristics to them. So, we hope for better, but fear worse. This is also the time for frightening predictions, about obesity, climate change, and sundry popular worries.

With that in mind, I predicted that hope would always predominate over fear, for the simple reason that reproduction requires optimism. I turned to N gram for confirmation, and found my views substantially confirmed. There was also a surprise: peaking in 1830, hope and fear have since been in free fall. Both words have reduced in frequency over 200 years, and by the Millennium were almost at par. Any reasonable computer model would have predicted fusion, or even a cross-over, with fear in the ascendant. For some reason there has been a rebound. Why?

It has nothing to do with the sin of greed, nor is it anything to do with optimism and pessimism. On this scale they are irrelevant. Neither do boom or bust figure, nor stocks or shares. Not even recession shows an effect.

Perhaps it is simply a song with those words in it, but we have begun to hope and fear again. Perhaps you can suggest why.


Thursday, 2 January 2014

PISA goes to US, finds little bang for buck


You may remember that I succumbed to PISA fatigue, and called for dedicated souls to help me churn through the remaining volumes. Andrew Sabisky (@AndrewSabisky) has stepped into the breach, so here is his take on Vol 5 in which PISA visits the US.

PISA 2012 Vol 5

America merits its own volume in the PISA reports, probably because its educational establishment is PISA’s largest customer. Education reformers, backed by the Obama administration, even put together their very own “PISA day” (which fell on December 3rd) to analyze (but not celebrate) America’s PISA results ( What message, then, did these ardent educationalists hear from PISA? What messages could they have heard, but, for lack of education, did not receive?

PISA 2012 largely focused on mathematics. America ranks 26th out of 34 participating OECD nations, though it does better in reading (17th) and science (21st). 26% of American 15-year-olds do not reach the PISA “level 2” yardstick of basic mathematical proficiency (OECD average 23%), though this figure falls to 16% after removing those students from an immigrant background. The definition of what counts as “an immigrant background” seems to be given nowhere. Just 2% of American students reach the top band (level 6), compared to 3% across the OECD and “up to 31%” in Shanghai.

These are the basic facts of the American PISA scores. It would seem, therefore, that taken as a group, American students are about average compared to those in other OECD nations, perhaps performing slightly worse in some respects. Of course, treating American students as one unitary group may hide significant and important within-group differences. America is a highly diverse nation, both racially and culturally, though PISA rarely allude to this fact. They do, however, note that Blacks and Hispanics are substantially overrepresented in the American population of low-skilled adults, as measured by PISA’s twin brother, the OECD Survey of Adult Skills (PIAAC). Skills, in the world of PISA, are regarded as all-important, though individual and group differences in the capability of learning certain skills are not considered. Steve Sailer has in fact found data dividing American PISA scores by race with enlightening results (

PISA also attempt to establish some rather less basic and more contentious facts. America apparently has fewer “resilient” students than other countries; just 5% compared to an OECD average of 7%, and between 15-20% in Vietnam, Hong Kong, and Shanghai. “Resilient” students are from the bottom quarter of the socioeconomic status scale (relative to their country of assessment), but who perform in the top quarter of students among all participating countries, after adjusting for socioeconomic status (emphasis added). Therefore, to be classed as resilient, a disadvantaged child does not have to actually score in the top quartile across all nations - he can score considerably less well, but PISA will helpfully bump his scores up. The ghost of the sociologist’s fallacy has returned with a vengeance. The possibility that a low percentage of “resilient” students may in fact function as an indicator of societal meritocracy is also not considered.

Other data, however, perhaps provide more basis for applicable conclusions. The first is that American education is inefficient. Only Norway, Austria, Luxembourg, and Switzerland spend more money per student than America, while nations such as the Slovak Republic spend less than half as much per student as America for the same PISA scores, while Korea also spends considerably less for chart-topping results. Perhaps American educators could safely return some of their budget to the taxpayer and the Gates Foundation, without fear of any loss of performance. There is a statistical relationship between mathematics performance in PISA and national spending on education (r squared = 0.3), though this may be accounted for by the relationship between national IQs and GDP. Cleverer nations, likely to perform better in maths, are also often the wealthier nations on account of their brighter, more productive citizens, and hence have more cash to spend on social goods such as education. PISA, is it worth pointing out, do not follow this line of analysis. America notably spends a higher percentage of its educational budget on “capital outlays” than its competitors (11.4% versus 8.7% OECD average). Perhaps the cash allocated to new school buildings, swanky sports fields, and iPads for all pupils in Los Angeles could be better spent elsewhere.

Does the school climate make a difference? American students are inclined to play truant: 20% have done so within the past two weeks, compared to an OECD average of 15%, and an average of under 5% in many Asian and some European nations. Do American students lack the foresight to make rational decisions in this matter? Perhaps some calculate they can learn more elsewhere? Perhaps some do so accurately. Nevertheless, despite their higher rates of truancy and lower performance, American students do not view their teachers in such a ghastly light; in fact, they view them rather positively, more so than in other OECD nations. 86% of American students think that their teachers are interested in their wellbeing, whereas just 59% of Japanese students do (OECD average 77%). American students also think highly of other aspects of their relationship with their teachers, such as the teachers’ ability to listen and willingness to give their students extra help. The cause of American underperformance cannot seem to be located here. American discipline also seems to be at least on par with the OECD average: 82% of American students report that classroom disruption so severe they cannot work never happens, or almost never happens, compared to an OECD average of 78%. School principals, however, are apparently less sanguine than students about American discipline, though the exact figures are for now lost to PISA’s endless appendices. Overall, the schools with the worst discipline tended to be those with the poorest pupils and the lowest scores, but the nation-level figures perhaps imply here that correlation does not lead us down the path of causation.

School governance is another hot-button topic in nations on both sides of the Atlantic, and here too PISA has some data for policymakers. School autonomy in resource allocation, curricula creation, and assessments apparently correlate positively with higher scores. This relationship persists after controlling for national income, though a correlation coefficient does not appear anywhere. Of course this finding is interpretable in many ways. School autonomy may lead to better results, or more intelligent teachers may demand and receive more freedom from state interference to educate their more intelligent students as they see fit. The usual non-relationship is found (after removing two outliers) between class size and test performance, though Asian nations typically do pay their high school teachers better than America does, whilst also trending towards larger class sizes.

The report also contains a chunky section entitled “Strengths and Weaknesses of American Students in Mathematics”. It runs to 30 pages of A4, but the substance of it is that American students do much worse (relative to Asian and other better-performing nations) on the harder, more cognitively complex PISA items, and do less badly on the easier items. One could interpret this as signifying that some significant amount of the difference between America and the nations that outperform it may be on psychometric g. PISA themselves, however, limit their conclusions to “the relative strengths of the United States lie mostly in the easy items” and “the United States has a particular weakness in the most challenging items”. This is a frustrating failure of analysis just as PISA’s data start to suggest an intriguing pattern worthy of further thought. It is hard to believe that none of the authors of the report had any kind of background in test design.

Lastly, the report attempts to analyze whether or not implementation of the Obama administration’s new “Common Core” universal standards will improve American performance in PISA mathematics. Purely in terms of test readiness, they may indeed do so to a small extent, since the Common Core standards have apparently been heavily drawn from those of PISA. Of course, this assumes the standards are implemented faithfully and without wavering if and when grades begin rapidly to deflate in the face of tougher exams. Experience would perhaps suggest that this is unlikely to occur. We shall see.

Despite its many inadequacies, including a complete failure to include genetic quality (intelligence A) as a variable contributing to both school outcomes and socioeconomic status, the PISA report on American education does retain some value. Most notably it highlights the high rate of financial waste for mediocre results, something the American taxpayer will be displeased to learn. The largely positive atmosphere in American schools does not seem to have much effect on outcomes. For both education reformers and anti-reformers alike, there is much to learn as they fight their never-ending war over the future of schooling in the world’s great power.