Razib Khan One-stop-shopping for all of my content

July 19, 2012

Cousin marriage can reduce I.Q. a lot

Filed under: I.Q.,Psychology — Razib Khan @ 11:33 pm

In light of the previous post I was curious about the literature on inbreeding depression of IQ. A literature search led me to conclude two things:

- This is not a sexy field. A lot of the results are old.

- The range in depression for first cousin marriages seems to be on the order of 2.5 to 10 IQ points. In other words ~0.15 to ~0.65 standard deviation units of decline in intelligence.

The most extreme case was this paper from 1993, Inbreeding depression and intelligence quotient among north Indian children. The authors compared the children of first cousin marriages, and non-bred in individuals, from a sample of Muslims in Uttar Pradesh of comparable socioeconomic status (though the authors note that inbreeding has a positive correlation with socioeconomic status in this community). A table with results speaks for itself:

January 28, 2012

Social conservatives have a lower I.Q.? (probably)

Filed under: conservative,Culture,I.Q.,Intelligence,Liberalism,Politics — Razib Khan @ 1:29 pm

In light of my previous posts on GRE scores and educational interests (by the way, Education Realist points out that the low GRE verbal scores are only marginally affected by international students) I was amused to see this write-up at LiveScience, Low IQ & Conservative Beliefs Linked to Prejudice. Naturally over at Jezebel there is a respectful treatment of this research. This is rather like the fact that people who would otherwise be skeptical of the predictive power of I.Q. tests become convinced of their precision of measurement when it comes to assessing whether a criminal facing the death penalty is mentally retarded or not! (also see this thread over at DailyKos). You can see some of the conservative response too.

The paper itself is Bright Minds and Dark Attitudes: Lower Cognitive Ability Predicts Greater Prejudice Through Right-Wing Ideology and Low Intergroup Contact:

Despite their important implications for interpersonal behaviors and relations, cognitive abilities have been largely ignored as explanations of prejudice. We proposed and tested mediation models in which lower cognitive ability predicts greater prejudice, an effect mediated through the endorsement of right-wing ideologies (social conservatism, right-wing authoritarianism) and low levels of contact with out-groups. In an analysis of two large-scale, nationally representative United Kingdom data sets (N = 15,874), we found that lower general intelligence (g) in childhood predicts greater racism in adulthood, and this effect was largely mediated via conservative ideology. A secondary analysis of a U.S. data set confirmed a predictive effect of poor abstract-reasoning skills on antihomosexual prejudice, a relation partially mediated by both authoritarianism and low levels of intergroup contact. All analyses controlled for education and socioeconomic status. Our results suggest that cognitive abilities play a critical, albeit underappreciated, role in prejudice. Consequently, we recommend a heightened focus on cognitive ability in research on prejudice and a better integration of cognitive ability into prejudice models.

I emphasized sections that I assume will answer some immediate questions, as not everyone has access to Psychological Science. Yes, they used different types of intelligence tests; verbal and spatial. Yes, they corrected for socioeconomic background. Their replication was in the UK and USA. Importantly, they focused on a few characteristics, attitudes toward homosexuals and race. It doesn’t seem like they explored an enormous range of opinions. And as noted in the paper they were looking at the social dimension of political ideology.

There is plenty of work on cognitive styles and political orientation. Recently it is moral foundations from Jon Haidt. Earlier you had George Lakoff’s models. Neither of these focused on general intelligence, the raw CPU power of the mind. Rather they surveyed moral intuition and personality profiles (for example, there is some evidence that those with a greater bias toward “openness” are more socially liberal).

Looking at the General Social Survey I too have found at a correlation between higher intelligence and social liberalism. On the other hand a good objection to this is that my estimator of intelligence, WORDSUM, was verbal, and liberals and conservatives may exhibit different cognitive profiles. This study takes that into account, adding spatial I.Q. tests to the mix.

It is important to emphasize that the authors do not posit an independent direct causal connection between low I.Q. and more reactionary attitudes towards race and homosexuality. Rather, they start out with a model where low cognitive ability people are drawn (or remain in) to conservative orientation, and this is further correlated with these specific racial and sexual attitudes. Like almost all psychology you can’t get the causation airtight (if you are a hardcore Humean you could probably say this for everything), but the correlation is suggestive in light of political and psychological models. The problem is the second. As Jonathan Haidth has articulated most recently most academic political scientists and psychologists have strongly social liberal views, and so they consciously or unconsciously tend to caricature and misrepresent the views of half their study population (notice that the authors assume that these socially conservative positions are ‘Dark Attitudes’; most people today would agree, but shouldn’t intellectuals avoid this sort of thing?). So though I have some confidence in the correlations, I’m a lot more skeptical of the explanatory models (though I don’t reject them out of had). There are so many models sitting around that how you chose models can be shaped by bias rather easily.

First, let’s hit the results.

The table above represents the results for the British cohorts and race, and the diagram to the left illustrates the outcome for the American sample and homosexuality. The primary point is that as per their hypothesis the effect of lower cognitive ability on prejudice toward other races and homosexuality is mediated more or less through ideology. Coarsely, stupid people aren’t racist, stupid people are more likely to be socially conservative, and more socially conservative people are more likely to be racist. How these join together though is something one can subject to more critical examination. The authors allude to this when they note that there is a finding that those who know people of other races tend to be less prejudiced, with the inference being that contact makes one less racist. But this is not an established causality. Rather, it could be that people with less prejudiced tendencies put themselves into situations where they are likely to meet other races. This tendency could be correlated with higher I.Q. through a mediation of a “cosmopolitanism index.” Who knows? There are many stories one could tell.

I do want to emphasize though that this is a coarse measure of ‘conservatism.’ In the early to mid aughts Paul Wolfowitz was a hated figure on the American political Left because of his critical role in buttressing the intellectual armamentarium favoring the invasion of Iraq. But it is well known that Wolfowitz was and is a social liberal, like a subset of neoconservatives who focus on foreign policy. On the above measure Wolfowitz, who has undergraduate degrees in mathematics and chemistry from Cornell and a graduate degree in political science from University of Chicago, would come out as a high I.Q. social liberal. Is that right? As far as it goes it is right, but on some level the results would be misleading in the more complex terrain of coalitional politics. A substantial number of Americans shake out as social conservatives and fiscal moderates/liberals. And yet this faction is totally unrepresented in modern politics. In contrast, their inverse, libertarians, do have some representation, albeit a marginalized one. Why? Because the latter position has modest high I.Q./elite support, while the former position has far less. If you changed the question to attitudes toward global free trade there would be a correlation between lower I.Q. and the ‘more liberal’ (at last in American politics) position.

This qualification also dovetails with the broader point about styles of cognitive thinking, and reliance on traditional norms as opposed to think a priori. Ironically it makes intuitive sense that higher I.Q. people would be less reliant on intuition, impulse, and collective wisdom. But there are limits to this. For example, see the reaction to the proposition of sex between consenting adults who happen to be siblings on an atheism forum (assume they use birth control). But some moral philosophers posit that this is not harmful or immoral, and should be socially accepted. It’s an interesting illustration of the boundary condition of the power of disgust and emotion, as only the hyper-rational feel comfortable even entertaining the moral legitimacy of this proposition. More relevantly, educated liberals also make use of ‘stereotypes’ constantly. It’s just that those stereotypes are of conservatives. I know this because almost all my friends are educated liberals, and they often forget that I’m a conservative. So I hear a lot about conservatives are this and that without qualification, to great merriment and laughter (also, conservatives are genuinely evil and malevolent apparently!). The tendency toward generalization doesn’t bother me in an of itself, rather, I’m focused on whether the proposition is true. But the hypocrisy gets tiresome sometimes, as people will fluidly switch from a cognitive style which accepts generalization to one which rejects it. A stereotype is often a generalization whose robustness you don’t want to accept. Negative generalities need context when they’re unpalatable, but no qualification is necessary when their truth is congenial. Sometimes this veers into moderately politically incorrect territory. I was once an observer on a conversation between liberal white academics who were mulling over the unfortunate reality that their Asian American students were far more likely to cheat to obtain better grades. I suspect that this is actually true for various reasons. But I also suspect that these academics forgot that I was privy to the conversation, and wouldn’t have aired this truth in a more racially diverse social context.

More broadly what is the takeaway from this sort of research? Should we conclude that because the more intelligent tend to be socially liberal that socially liberal propositions are true? I think one should be skeptical of this position. There are two immediate rejoinders. First, politics is a matter of values. The reliance of reason vs. emotion, individual ratiocination vs. historical or social wisdom, may vary. But that does not speak to the truth of any given value judgement, as those judgments are embedded in a system of norms, as well as individual self-interest (e.g., the higher I.Q. tendency to favorable attitudes toward free trade may have less to do with an understanding of comparative advantage, than an implicit understanding that globalization favors them as opposed to less intelligent lower classes). Second, the moral arc of history is not always unidirectional. The ‘progressive’ position is sometimes reversed. In Better for All the World there is a broad history of the rise of a consensus among economic and intellectual elites about the wisdom of coercive eugenics as an instrument of progressive social engineering in the late 19th century. Religious conservatives, whether evangelical Protestant or Roman Catholic, were two of the greatest bulwarks against this force for progress. Arguably these two elements were more efficacious in resisting the spread of eugenics legislation than the Left critics, judging by the outcomes Southern Europe and the American South, as opposed to the more ‘forward thinking’ nation-states of Northern Europe and the American North. This fact is unknown to most of my friends and acquaintances, judging by repeated assumptions that any utilization of personal genomics for eugenic purposes will occur first in politically conservative jurisdictions.

With all these qualifications, I believe this sort of research is essential and insightful. We need to understand the patterns of cognitive variation, whether it be intelligence or personality, which may result in differences of opinion. At the end of the day no opinions may change, but one may be able to construct a crisper argument when taking into account the genuine roots of one’s political opponents viewpoints, rather than your own ill-informed caricature.

Addendum: I did not address the issue of revealed vs. avowed preferences and attitudes. But I think that this difference will not change the sign of correlation. For example, for various reasons I assume that the gap between white liberals and white conservatives when it comes to race is smaller in terms of the preference revealed in their choices, rather than the survey responses they give, but I don’t think it reverses the rank order of the correlation.

Citation: Bright Minds and Dark Attitudes: Lower Cognitive Ability Predicts Greater Prejudice Through Right-Wing Ideology and Low Intergroup Contact, Psychol Sci. 2012 Jan 5.

December 30, 2011

Vocab by ethnicity, region, and education

Filed under: data,Data Analysis,GSS,I.Q.,Regionalism — Razib Khan @ 12:58 pm

A questioner below was curious if vocabulary test differences by ethnic and region persist across income. There’s a problem with this. First, the INCOME variable isn’t very fine-grained (there is a catchall $30,000 or greater category). Second, it doesn’t seem to control for inflation. But, there is a variable, DEGREE, which asks the highest level of education attained. I used this to create a “college” and “non-college” category (i.e., do you have a bachelor’s degree or not). Because of sample size considerations I removed some of the ethnic groups, but replicated the earlier analysis.

Below are two tables. One shows the mean vocab score for region and ethnicity (for whites) for those without college educations, and another shows those with college educations. I decided to generate a correlation over the two rows, even though it sure isn’t useful as a quantitative statistical measure because of the small number of data points. Rather, I just wanted a summary of the qualitative result. The short answer is that the average vocabulary difference seems to persist across educational levels (the exception here is the “German” ethnicity).

Mean WORDSUM Score by Ethnicity and Region
No college education




German 6.05 5.81 5.79 6.11
Eastern Europe 6.17 6.16 6.18 6.29
Scandinavian 6.35 5.97 6.23 6.35
British 6.6 6.21 6.02 6.57
Irish 6.66 5.83 5.69 6.58
Italian 6 5.85 5.8 6.18

College educated




German 8.03 7.48 7.63 7.33
Eastern Europe 7.7 7.37 7.5 8.09
Scandinavian 8.5 7.82 7.86 7.92
British 8.44 8.06 7.76 7.95
Irish 8.03 7.79 7.39 7.59
Italian 7.45 7.75 7.6 7.87

Correlation of college and non-college
German 0.08
Eastern Europe 0.92
Scandinavian 0.57
British 0.70
Irish 0.57
Italian 0.40

December 11, 2011

Most Reported Genetic Associations with General Intelligence Are Probably False Positives

Filed under: Behavior Genetics,Genomics,Human Genomics,I.Q.,Psychology — Razib Khan @ 4:49 pm

The title says it all, and I yanked it from a paper that is now online (and free). It’s of interest because of its relevance to the future genetic understanding of complex cognitive and behavioral traits. Here’s the abstract:

General intelligence (g) and virtually all other behavioral traits are heritable. Associations between g and specific single-nucleotide polymorphisms (SNPs) in several candidate genes involved in brain function have been reported. We sought to replicate published associations between 12 specific genetic variants and g using three independent, well-characterized, longitudinal datasets of 5571, 1759, and 2441 individuals. Of 32 independent tests across all three datasets, only one was nominally significant at the p ~ .05 level. By contrast, power analyses showed that we should have expected 10–15 significant associations, given reasonable assumptions for genotype effect sizes. As positive controls, we confirmed accepted genetic associations for Alzheimer disease and body mass index, and we used SNP-based relatedness calculations to replicate estimates that about half of the variance in g is accounted for by common genetic variation among individuals. We conclude that different approaches than candidate genes are needed in the molecular genetics of psychology and social science.

My hunch is that these results will be unsatisfying to many people. The authors confirm and reassert the heritability of general intelligence, both by reiterating classical results, and utilizing novel genomic techniques. But, they also suggest that the candidate gene literature is nearly worthless because of the lack of power of most of the earlier studies. The latter is probably due to the genetic architecture of the trait. Intelligence may be determined by numerous genes of very small effect (e.g., 0.01% of the variance effected by one particular SNP), or, “rare, perhaps structural, genetic variants with modest to large effect sizes.” The former case is pretty obvious, but what about the latter? I’m mildly skeptical of this because I’m curious why modest-to-large effect variants didn’t show up in family-based studies (presumably within the family the same variants would localize to sections of the genetic map)? But I’m not fluent enough in the literature to know if there was a lot of work in this area with families previously.

Related: Here’s the first author’s article in Commentary from the late 1990s, IQ Since “The Bell Curve”.

September 25, 2011

Like modestly attracts like

Filed under: I.Q.,marriage,Psychology,Sociology — Razib Khan @ 11:04 pm

I saw this link posted on twitter, IQ and Human Intelligence:

An interesting finding from genetic research, which Mackintosh mentions, only in passing, as posing a problem in the estimation of the heritability of g, is that there is greater assortative mating for g than for any other behavioral trait; that is, spouse correlations are only ∼.1 for personality and only ∼.2 for height or weight, but the correlation for assortative mating for g is ∼.4. In addition to indicating that people are able to make judgments about g in real life, this finding suggests that assortative mating may contribute to the substantial additive genetic variance for g, because positive assortative mating for a character can increase its additive genetic variance.

I’ve seen these sort of results before. The review is from 1999. In general I always wonder if quantitative values for personality are not to be trusted because of issues with the measurement of personality types. But this is clearly not an issue with height or weight. And in the case of height the overwhelming causal explanation for variation in the West is genetic variation. Overall I’m rather surprised by the rather low correlations for some of these traits, such as height and intelligence. I wonder if beauty, perhaps measured by an index of facial symmetry, might exhibit higher correlation values?

August 10, 2011

Half the variation in I.Q. due to variation in genes

A new paper in Molecular Psychiatry has been reported on extensively in the media, and readers have mentioned it several times in the comments. I read it. It’s titled Genome-wide association studies establish that human intelligence is highly heritable and polygenic. But the fact is that I read this paper last year. Back then it was titled Common SNPs explain a large proportion of the heritability for human height. I kid, but you get the picture. The new paper establishes for intelligence what we already suspected: most of the genetic variation in this heritable trait is accounted for by numerous genes of small effect. You inherit variants of these numerous genes from your two parents, and your own trait value is to a large extent a combination of the parental values. The issue is not if intelligence is heritable, but the extent of that heritability.

The standard way to estimate human heritability was to track similarities across individuals with varying degrees of relatedness. For example, compare identical twin correlations on a trait with fraternal twin correlations. The main objection to these methods is that one could argue ...

August 5, 2011

South Asian I.Q.

Filed under: Culture,I.Q. — Razib Khan @ 7:10 pm

Check out the discussion at Steve Sailer’s weblog. People always ask my opinion on this issue. All I’d say is this: don’t bet against the Chinese.

June 16, 2011

Parents don’t matter that much

Update: Stephen Dubner emailed me, and pointed me to this much longer segment which has a lot of Bryan Caplan. So it seems like the omission that I perceived was more of an issue with the production and editing process and constraints of the Marketplace segment than anything else.

End Update

I play a lot of podcasts during the day as I go about my business on my iPod shuffle. One of them is Marketplace, which has a regular Freakonomics Radio segment, where Stephen Dubner “freaks” you out with incredible facts and analysis, often with a helping hand from Steven Levitt. With all due respect to Dubner and Levitt, this still has very pre-Lehman feel. Economics has “solved” the workings of the explicit market, so why not move on to other areas which are ripe for conquest by the “logic of life?”

In any case this week’s episode kind of ticked me off just a little. It started off with the observation that college educated women apparently put 22 hours weekly into childcare today, vs. 13 hours in the 1980s. I guess fewer latchkey kids and more “helicopter parents?” Dubner basically indicates that the reasoning ...

May 13, 2011

I.Q. and genomics

Filed under: B.G.I.,Behavior Genetics,Genomics,I.Q.,Psychology,Psychometrics — Razib Khan @ 9:15 pm

In my experience most scientists are not too clear on the details of intelligence testing, perhaps because the whole area is somewhat in ill repute (except when you want to brag about your own SAT/GRE score!). This despite the fact that the profession of science is skewed toward the right end of the intelligence bell curve. Steve Hsu, a physicist at the University of Oregon (and someone I’ve known for a while in the interests of “full disclosure”) has a nice presentation up in PDF format which summarizes the major points of interest in this area. Worth a skim if you are unfamiliar. Additionally he alludes to future directions in the study of the genetic basis of intelligence using genomics. Here’s his abstract:

I begin with a brief review of psychometric results concerning intelligence (sometimes referred to as the g factor, or IQ). The main results concern the stability, validity (predictive power) and heritability of adult IQ. Next, I discuss ongoing Genome Wide Association Studies which investigate the genetic basis of intelligence. Due mainly to the rapidly decreasing cost of sequencing (currently below $5k per genome), it is likely that within the next 5-10 years we will identify genes ...

January 21, 2011

The stupid rich and poor smart do exist

Filed under: Data Analysis,I.Q.,WORDSUM — Razib Khan @ 12:56 am

WORDSUM is a variable in the General Social Survey. It is a 10 word vocabulary test. A score of 10 is perfect. A score of 0 means you didn’t know any of the vocabulary words. WORDSUM has a correlation of 0.71 with general intelligence. In other words, variation of WORDSUM can explain 50% of the variation of general intelligence. To the left is a distribution of WORDSUM results from the 2000s. As you can see, a score of 7 is modal. In the treatment below I will label 0-4 “Dumb,” 5-7 “Not Dumb,” and 8-10 “Smart.” Who says I’m not charitable? You also probably know that general intelligence has some correlation with income and wealth. But to what extent? One way you can look at this is inspecting the SEI variable in the GSS, which combines both monetary and non-monetary status and achievement, and see how it relates to WORDSUM. The correlation is 0.38. It’s there, but not that strong.

To further explore the issue I want to focus on two GSS variables, WEALTH and INCOME. WEALTH was asked in 2006, and it has a lot of categories of ...

January 12, 2011

When genes matter for intelligence

Filed under: Behavior Genetics,Genetics,Heritability,I.Q.,Psychology — Razib Khan @ 3:01 am

Image credit: Aleksandra Pospiech

One of the interesting and robust nuggets from behavior genetics is that heritability of psychological traits increases as one ages. Imagine for example you have a cohort of individuals you follow over their lives. At the age of 1 the heritability of I.Q. may be ~20%. This means that ~20% of the variation in the population of I.Q. explained by variation in the genes of the population. More concretely, you would only expect a weak parent-offspring correlation in I.Q. in this sample. At the age of 10 the heritability of I.Q. in the same sample may be ~40%, and in mature adulthood it may rise to ~80% (those are real numbers which I’ve borrowed from Robert Plomin). Many people find this result rather counterintuitive. How can a trait like intelligence become “more genetic”?

Remember that I’m talking about heritability here, not an ineffable “more” or “less” quantum of “genetic” aspect of a trait. In other words: does variation in genes due to different parental backgrounds matter for a trait? Second, the nature of psychological traits is somewhat slippery and plastic. As I’ve noted before the correlation between a score on a 10-world vocabulary test and general intelligence is pretty good. You can expect people with high scores on the vocabulary test to have higher I.Q.’s than those who have low scores. But if you take an individual and lock them in a room without human contact for their first 15 years, they are unlikely to exhibit any such correspondence. You don’t have to be a rocket scientist to understand why. Quantitative behavior genetic traits are complex and are subject to a host of background conditions, and express themselves in an environmental context.

So why can you explain more of the variance of a psychological trait like I.Q. at age 40 than at age 5 with genes? It has to do with environment. Specifically, intelligence isn’t something you’re born with, it’s something that you develop over time, through a complex confluence between biology and environment. The developmental process exhibits a level of contingency as well. Decision A redounds to the choice between B and C, which redounds between a further set of choices. Small initial differences in disposition and talent can compound over time through positive feedback loops. Practice may make perfect, but perfection may be a goal to which you aspire only if you have initial talent or inclination.

In other words, your genetic disposition can shape the environment you select, which can then serve to express your genetic potential in a specific manner. Children have less power in selection of their environment than adults. Over time the model is that environmental variables which differentiate children diminish in importance as they select contexts and situations which express their own preference sets as adults. This dynamic can be illustrated with a rather strange example. Consider two siblings who are pressured to be academic by their parents. One has a natural disposition toward scholarly activities, while the other does not. Their realized performance difference in youth may be small. People can respond to incentives! But at 18 the two siblings become adults, and begin to make their own decisions. At 25 one sibling may be a university drop out, and the other a graduate student. The modest differences in adolescence may start amplifying due to the positive feedback loops which consist of a set of choices which exhibit dependencies. Of course siblings would tend to be more similar than two random individuals off the street. But even within families there is genetic variance and so innate differences of disposition (the average difference in I.Q. between siblings is about the same as the average difference in I.Q. between two random people off the street, one standard deviation, or 15 points).

ResearchBlogging.orgModeling behavior genetic phenomena in a rough & ready fashion is then a matter of keeping dynamic networks of parameters in your head. Traits aren’t constructed about of static blocks; they’re the outcomes of a set of parameters at a given moment, as well as a developmental arc shaped by a previous set of parameters (some of them the same, some of them new). Thinking like this gives you a method by which to analyze phenomena, it does not tell you in a clear and general manner how a whole range of phenomena emerged down to the last detail.

The analysis doesn’t just apply to populations over time. You can also look to different groups which are contemporary. In 2003 a paper was published, Socioeconomic Status Modifies Heritability of IQ in Young Children. The major findings are illustrated by this figure (I’ve added some clarifying labels):

On the x-axis you see socioeconomic status (SES). This variable is a compound of traits which reflect’s one’s position in the social status hierarchy. Income and wealth are clearly important, but a salesman for a fertilizer company could presumably be more economically well off than a physics professor. So other variables such as education also matter. It is clear then that as SES increases genetic variation explains much more of the variation in I.Q., while environment explains less and less. The shared environment is rather straightforward: your family. The non-shared environment is more vague, and to some extent is just the remainder from the model which predicts I.Q. In The Nurture Assumption Judith Rich Harris posited that non-shared environment was mostly peer group effects. Interestingly, by adulthood non-shared environment tends to be a more important variable than shared environment for most psychological traits.

Any guess for why genetic variance is more efficacious in prediction of I.Q. among the high status than the low status? Here’s a clue: heritability of height is much higher in developed nations than in developing nations. In other words, environment explains more of the variance in height in developing nations, while it explains almost none of the height in developed nations. There’s only so much you can eat, and there are diminishing returns on nutritional inputs. In developed nations most of the environmental variance has been removed due to adequate nutrition. When you remove the environmental variance, the genetic variance remains. Heritability is roughly the ratio of the additive genetic variance over the total variance, so its value gets larger.

The analogy to I.Q. should be relatively easy. Don’t tell Amy Chua, but there are probably diminishing marginal returns on “nurturing” environments for a child when it comes to their intellectual development. You have only a maximum of 24 hours in the day you can study and drill, and a personal library of 10,000 is probably not very different from 1,000, if all the books fall within the purview of your interest. Even in well off suburban communities there are differences of wealth and income, but on the margin vast increases in wealth and income do not allow one’s child to develop their mental faculties proportionality greater. What there remains in well off suburban communities are differences of genetic disposition and aptitude. Bill Gates’ children are probably good candidates for the Ivy League. Not because he is worth billions of dollars in relation to a professional whose net assets barely break a million. Gates got into Harvard, and reputedly did well before dropping out to pursue his business. His wife is also an overachiever.

This is I believe a fascinating topic, and needs to be explored in more detail. Some members of the same group now have a study out which shows that differences in socioeconomic status matter differently for infants at 10 months and tots are 2 years. Emergence of a Gene × Socioeconomic Status Interaction on Infant Mental Ability Between 10 Months and 2 Years:

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. 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.

They used a standard SEM model. I’m not going to go over that in detail, but suffice it to say that they related a set of variables to the outputs which they wanted to predict, performance on I.Q. tests for very young children. If you are curious, the demographic sample was rather diverse, and controlling for race did not impact their outcomes. So let’s outline what’s going on here.

First, predicted:

- Performance at 10 months
- Performance at 2 years

Second, putative predictors:

- Genes (A). Specifically, additive genetic variance
- Shared environment (C)
- Non-shared environment (E)

I’ve reedited some of the main results. On the Y axis you see the % of variance explainable by A, C, and E. The variance components are broken down into two levels: SES, and age. 2 SD means 2 standard deviations. In a normal distribution that’s the ~2% tail at the ends.

What you see are two trends with age and SES:

- For infants at the age of 10 months parents matter. Genes do not. SES is not a major issue.

- For tots at the age of 2 years, SES matters quite a bit. You see a recapitulation with the earlier data, where higher SES parents seem to be providing environments which probably exhibit diminishing marginal returns (environmental variance doesn’t have much of an effect on the margin), so that genetic variance is much more important by default. The trend is clear as you move in a step-wise fashio up the class ladder. Though I have to say, the top ~2% in SES is an elite group already, so I wonder what sort of environmental variance could be found there.

The figure to the left shows the same outcome out of their model, only now the curves illustartes the variation of the effects as you modify SES in a continuous fashion. These are estimates generated out of their model, so that probably explains the > 100% values you see on the margins. The key is to focus on the broad qualitative trends. Even at 2 years of age genes start to trump shared environment ~1 standard deviation above the norm (though not aggregate “environment”). If the earlier data is correct, the heritability will continue to increase over time for higher SES individuals, as their affluent backgrounds will give them perfect freedom to take them where their dispositions lead them.

Why does all this matter? There are practical outcomes to this sort of research. I’ll quite from the paper:

These findings build on a growing body of literature that highlights the importance of early life experiences for cognitive development…Current evidence suggests that, although children maintain a great deal of neurobiological and behavioral plasticity well past infancy…the predictive validity of infant mental ability for later cognitive ability is moderate…We agree with Bornstein and Sigman…who have strongly argued against the perspective “that infancy might play little or no role in determining the eventual cognitive performance of the child and, therefore, that individuals could sustain neglect in infancy if remediation were later made available”…Heckman…has recently taken an economic perspective on this topic. He argued that prophylactic interventions for disadvantaged younger children produce much higher rates of return on what he termed “human skill formation” than later remedial interventions for older children and adults do. On the basis of this perspective, Heckman concluded that “at current levels of funding, we overinvest in most schooling and post-schooling programs and underinvest in preschool programs for disadvantaged persons”….

My understanding is that the long-term effectiveness of even Head Start is non-existent, so I don’t know what proposals could be made based on this. Preschool for 1-2 years? I find it broadly plausible that high SES parents do provide more enriching environments, but I don’t see the detailed understanding necessary for genuinely effective prescriptions. Rather, we’re doing conventional trial & error when it comes to policy.

Additionally, the authors also admit that the high and low SES populations may have been stratified for genes. That’s just a way of saying that it isn’t as if genetic variance for things like intelligence are necessarily equally distributed across the social classes. If a genuine meritocracy exists what one should rapidly see is a crystallization of hereditary class castes, as individuals marry and associate assortatively on a meritocratic basis. Remember, assortative mating should increase heritability estimates (Quantitative Genetics says so!). This is part of the irony of some peoples’ conception of how genes relate to outcomes. Equality of opportunity will almost certainly lead to a cleaner separation of outcomes by genetic variation. In a chaotic world defined by random acts many people will find themselves in positions at variance with their aptitudes or dispositions. Once you remove the environmental randomness, then from each according to their capabilities should be the outcome.

For future investigation: the hypothesis that Goldman Sachs partners are precursors to Guild Navigators!

Citation: Tucker-Drob EM, Rhemtulla M, Harden KP, Turkheimer E, & Fask D (2010). Emergence of a Gene x Socioeconomic Status Interaction on Infant Mental Ability Between 10 Months and 2 Years. Psychological science : a journal of the American Psychological Society / APS PMID: 21169524

July 28, 2010

Investing in a nanny state for social returns

Jonah Lehrer has a post up, How Preschool Changes the Brain over at Frontal Cortex. He reports on a paper, Investing in our young people, which has been around for about 5 years. The top line of it is this, an investment in a $2,500/year (inflation adjusted) pre-school program in the early 1960s seems to have been effective in improving the life outcomes of at-risk low SES young black Americans tracked over their lives up to the age of 40. Their measured I.Q.s were not initially high, 85-75, 15th to the 5th percentile (though the median black American IQ is ~85, so not so low within ethnic group). They did gain an initial I.Q. boost, but like most of these programs that boost disappeared over time. But in terms of their non-cognitive skills there remained an appreciable effect which impact their life outcomes. What were these non-cognitive skills? To me they resemble classical bourgeois values rooted in low time preference. Willing to be a “grind,” work hard and forgo short-term pleasures and not cave in to impulses with short-term gains and long-term costs.

Here’s a figure from the paper which I’ve reedited with labels:


Intuitively we understand this. Through experience we know of this. There are individuals with high intellectual aptitudes who lack self-control. Who do not succeed in life because of poor life choices. There are individuals with mediocre intellectual aptitudes who achieve a certain amount of comfort and prestige in their life because of their rock solid focus on their goals. By analogy an old under-powered computer with Ubuntu installed on it running Open Office will still perform at a higher level in achieving productivity goals than a high-powered computer which is loaded with Windows riddled with spyware and mostly running games which require a lot of computational muscle power beyond the specs of the box.

My main question is one of interpretation: is the change in non-cognitive skill portfolio due to intervention at a “critical period” in a neurobiological sense? The authors make explicit analogy to language. If children are exposed to a language before the age of 12 they generally can learn and speak it without an accent with marginal effort. Severely abused, or in rarer cases “feral children,” who are not exposed to language at all in their formative years, may remain unable to speak fluently in any language for the rest of their years after recontact with mainstream society. This is likely a function of the biological aspect of language acquisition and learning. Or at least that is the contemporary consensus.

Does this apply to non-cognitive skills? I am moderately skeptical, though my attitude here is provisional at best. Through the pre-prints the authors take a methodological individualistic perspective. Individuals invest in their skills, and the earlier they invest in their skills the more positive feedback loops can emerge so that their skills can mature, extend and sharpen. There’s clearly something to this. But the focus on family environment and such in the paper makes me a touch skeptical. There is a large behavior genetic literature which suggests that family environment, “shared environment,” is not very predictive of long term outcomes. Rather, “non-shared environment” explained about 1/2 of the outcomes for many behavioral traits (the balance is genetic variation).

In The Nurture Assumption Judith Rich Harris argued that the non-shared environment really referred to peer groups. Again, the analogy to language is illustrative. Children do not speak with the accent of their parents, they speak with the accent of their peer groups. There is an exception to this: autistic children (or, children who consciously want to have a particular affect). Though I was not explicit, this is the sort of dynamic I was indicating when I suggested that culture matters in saving. Different cultures have different norms, values, and frameworks in which you can express your personality predispositions. In genetic terminology I’m talking about a norm of reaction.

Quickly skimming through the original paper which Jonah Lehrer’s post was based on (and skipping over the guts of the economic modeling) I was unclear if there was a long-term peer group effect, as they didn’t seem to explore this possibility. Perhaps instead of a critical period in a neurobiological sense, what we’re seeing here is the emergence of specific peer groups which reinforce and buffer individuals in decision making and goal setting? Perhaps the original intervention resulted in the emergence of a new subculture within the low SES black community of Ypsilanti, Michigan?

Life outcomes can vary a great deal based simply on social norms.


In terms of the bottom line this may not change the policy conclusion that much. The operational outcome of a given policy may be the same even if the means by which the outcomes are realized differ. That being said, I probably does matter on the margins if the effect is due to individual level biological changes vs. group level norm shifts when it comes to details of policy formation.

Image Credit: CDC

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