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The Politics of the Null Hypothesis

The views expressed are those of the author and are not necessarily those of Scientific American.

Email   PrintPrint To what degree these and other differences originate in biology must be determined by research, not fatwa. History tells us that how much we want to believe a proposition is not a reliable guide as to whether it is true.Steven Pinker, commenting on Lawrence Summers in the The New Republic

In late April, Dr. Angela Lee Duckworth and her team published a study demonstrating that some of the variability in IQ test results–and in the life outcomes known to be correlated with IQ scores–varied significantly and substantially as a function of how motivated the test subject was. As the author herself points out in the paper, this is a fairly humdrum result. Those who developed IQ testing predicted that this would happen:


Despite efforts to "encourage in order that every one may do his best" on intelligence tests (ref. 41, p. 122), pioneers in intelligence testing took seriously the possibility that test takers might not, in fact, exert maximal effort. Thorndike, for instance, pointed out that although "all our measurements assume that the individual in question tries as hard as he can to make as high a score as possible . . . we rarely know the relation of any person’s effort to his maximum possible effort" (ref. 42, p. 228). Likewise, Wechsler recognized that intelligence is not all that intelligence tests test: "from 30% to 50% of the total factorial variance [in intelligence test scores remains] unaccounted for . . .this residual variance is largely contributed by such factors as drive, energy, impulsiveness, etc. . . ." (ref. 9, p. 444).

Yet this study that should be eliciting simple head nods was published in PNAS and is generating a fair amount of buzz. Ed Yong covers it nicely, emphasizing both underlying ability and motivation as factors in test results and educational and employment outcomes. ScienceNOW reports the findings, and Maria Konnikova of Artful Choice notes that motivation is a factor over which society has a certain amount of control.

The study is also receiving less positive notices. Steve Sailer at VDARE says the study tell us nothing new because IQ tests are still predictive, despite the researchers’ determination that a model that includes motivation predicts life outcomes better than one that doesn’t. StatSquatch runs a separate analysis taking out some of the data, but declines to submit the analysis as a peer-reviewed comment on the paper. And at EconLog, Bryan Caplan also visits the motivation factor:

For example, instead of saying, "IQ tests show that people are poor because they’re less intelligent – and intelligence is hard to durably raise" we should say, "IQ tests show that people are poor because they’re less intelligent and less motivated – and intelligence and motivation are hard to durable raise." If, like me, you already believed in the Conscientiousness-poverty connection, that’s no surprise.

The interesting thing about the disparity in views on this "non-controversial" study is how the views are divided. The straightforward reporting comes from science sites. The criticisms and assertions that the results are meaningless come from a linked group of political blogs. VDARE is an anti-immigration site; EconLog is a an economics blog. StatSquatch is perhaps most easily defined by the rate at which those on the blogroll perspire over "political correctness."

It seems that Pinker’s concerns that political influences may attempt to stifle science, noted in the quote at the top of this post, have some basis in fact. However, despite the direction of his concerns, those political influences in this case aren’t coming from the left, and they aren’t reflecting any anti-genetic bias. In fact, the comments on some of the coverage strongly demonstrate that it is Duckworth’s "position" that is presumed to be inherently flawed:

Thanks. I’ve been meaning to look at the individual studies in Duckworth’s paper myself, because her results simply seemed implausible. She is something of an anti-IQ warrior, and has published sloppy studies before, too.

It’s interesting that when a non-specialist journal publishes a paper on IQ, it’s almost always something that tries to question and minimize the significance of IQ. [source]

The vast majority of papers on IQ that make it to publication outside of specialist venues are those that take a contemptuous attitude towards the topic and refuse to engage the totality of evidence. In the meantime Paul Thompson at UCLA and BGI are respectively moving forward the IQ/neuroscience and IQ/genomics fields respectively. Keep pretending that doesn’t exist. [source]

Nothing about the field of IQ studies is free of political influence. It’s naive to believe that any kind of research on a purported measure of individual merit could be politics-free in a self-proclaimed meritocracy with wide inequalities. Binet’s original work was meant to determine which children should have access to additional educational resources. IQ scores are used occasionally to sort out "inappropriate" candidates for various jobs, including those whose IQs are too high for a role. IQ as a proxy for merit is used to argue that a group does or does not face discrimination in educational or career opportunities. This is all terribly political.

The question isn’t whether there are politics surrounding this issue or where. They’re everywhere. The question is where does the politics get in the way of the science? Again, the answers don’t favor Pinker’s view of a fatwa against genetic explanations of individual differences.

No one is pretending BGI Hong Kong doesn’t exist or that it isn’t looking for genes associated with variability in IQ scores. No one is issuing fatwas to stop them or even protesting their work. Some people are questioning IQ as a proxy for intelligence, but no one is saying the work shouldn’t go forward until a better proxy is found. Similarly, no one is pretending that Paul Thompson isn’t doing some fascinating work in brain imaging and variability in brain structure.

What is in dispute is the likelihood that genes will be found that account for any significant fraction of the variability found in human intelligence and whether the current literature on the topic is sufficient to predict that. Here is where disagreement with Thompson comes into play. He has published a number of papers with "genetics" in the title ("Genetic influences on brain structure," "Genetics of brain structure and intelligence," "Genetics of brain fiber architecture and intellectual performance") that involve no genetic testing whatsoever.

Instead, these studies rely on degree of relatedness (usually between identical and fraternal twins) as a measure of shared genes. This sounds reasonable, and to a degree it is. However, unless researchers can measure or control for the way genes unrelated to intelligence interact with the environment, these studies can’t tell us how much variation in brain structure is due to shared genes that code for intelligence and shared genes that code for something else, such as illness that limits time in school. Until these studies are designed to look for genetic influences in addition to environmental influences, these studies are useless for their intended purpose.

The degree of shared environment is a problem for studies of twins raised apart, as well. In 2001, Jay Joseph published a critique of these studies. It noted that the term "raised apart" has very little meaning for many of these pairs of twins: separated at a late age or brief period of years or placed with relatives in the same town. He also noted what a twin study that could control for environment would look like:

Although no conclusions about genetic influences on personality differences can be drawn from the MISTRA data, a description of a valid MZA study seems in order. First, a systematic ascertainment of twins would be undertaken. In addition to Juel-Nielsen’s (1965/1980) criteria that the twins be alive, reared apart from early life, and monozygotic, the twins must not have been aware of each other’s existence until they are contacted by the researchers. As a way of determining whether selective placement had occurred in the sample, each twin pair’s rearing-family socioeconomic status would be ranked and correlated. Once an experimental group of MZAs is collected in this manner, it would be compared with a control group of biologically unrelated pairs of strangers sharing the following characteristics: They should be the same age, they should be the same sex, they should be the same ethnicity, the correlation of their rearing environment socioeconomic status should be similar to that of the MZA group, they should be similar in appearance and attractiveness as determined by blinded raters, and the degree of similarity of their cultural backgrounds should be equal to that of the MZA twins. Finally, they should have no contact with each other until after they are evaluated and tested. These controls will constitute the unrelated group. Of course, it is not possible for unrelated pairs to share a common prenatal environment, which twins do share.

Cosma Shalizi, a professor of statistics who deals with the statistics of complex networks, also explains why the current literature is insufficient to support claims that genetic differences underlie observed differences in IQ scores. The article itself is technical, but the conclusions are fairly simple to follow:

1. The most common formulae used to estimate heritability are wrong, either for trivial mathematical reasons (such as the upward bias in the difference between monozygotic and dizygotic twins’ correlations), or for substantive ones (the covariance of monozygotic twins raised apart neglects shared environments other than the family, such as maternal and community effects)

2. The best estimate I can find puts the narrow heritability of IQ at around 0.34 and the broad heritability at 0.48.

3. Even this estimate neglected heteroskedasticity, gene-environment interactions, gene-environment covariance, the existence of shared environment beyond the family, and the possibility that the samples being used are not representative of the broader population.

4. Now that people are finally beginning to model gene-environment interactions, even in very crude ways, they find it matters a lot. Recall that Turkheimer et al. found a heritability which rose monotonically with socioeconomic status, starting around zero at low status and going up to around 0.8 at high status. Even this is probably an over-estimate, since it neglected maternal effects and other shared non-familial environment, correlations between variance components, etc. Under such circumstances, talking about "the" heritability of IQ is nonsense. Actual geneticists have been saying as much since Dobzhansky at least.

5. Applying the usual heritability estimators to traits which are shaped at least in part by cultural transmission, a.k.a. traditions, is very apt to confuse tradition with genetics. The usual twin studies do not solve this problem. Studies which could don’t seem to have been done.

6. Heritability is completely irrelevant to malleability or plasticity; every possible combination of high and low heritability, and high and low malleability, is not only logically possible but also observed.

7. Randomized experiments, natural experiments and the Flynn Effect all show what competent regressions also suggest, namely that IQ is, indeed, responsive to purely environmental interventions.

Despite the fact that these studies do not and cannot tell us that there is a genetic component to the variation in IQ, we still see genetic triumphalism like this 2009 article in The Economist.

Human geneticists have reached a private crisis of conscience, and it will become public knowledge in 2010. The crisis has depressing health implications and alarming political ones. In a nutshell: the new genetics will reveal much less than hoped about how to cure disease, and much more than feared about human evolution and inequality, including genetic differences between classes, ethnicities and races.


The trouble is, the resequencing data will reveal much more about human evolutionary history and ethnic differences than they will about disease genes. Once enough DNA is analysed around the world, science will have a panoramic view of human genetic variation across races, ethnicities and regions. We will start reconstructing a detailed family tree that links all living humans, discovering many surprises about mis-attributed paternity and covert mating between classes, castes, regions and ethnicities.

We will also identify the many genes that create physical and mental differences across populations, and we will be able to estimate when those genes arose. Some of those differences probably occurred very recently, within recorded history. Gregory Cochran and Henry Harpending argued in "The 10,000 Year Explosion" that some human groups experienced a vastly accelerated rate of evolutionary change within the past few thousand years, benefiting from the new genetic diversity created within far larger populations, and in response to the new survival, social and reproductive challenges of agriculture, cities, divisions of labour and social classes. Others did not experience these changes until the past few hundred years when they were subject to contact, colonisation and, all too often, extermination.

Well, it’s now 2011, and we have yet to see any crises. We’ve yet to see any replicated gene-intelligence associations. We’ve yet to see anyone step up to do, or even fund, the kinds of studies (aside from direct genetic testing) that would be required to differentiate genetic effects from environmental effects. We’ve yet to see the kind of doubt in these researchers that leads to studies that test hypotheses rather than reinforce conclusions. We’ve yet to see any lessening of the certainty that these much-sought genes are just around this next corner…oh…well, then, the corner after that.

What we have seen is yet one more study that shows a significant environmental element that accounts for some of the variability in IQ scores. And here is where we’ve seen political condemnation–of the researcher, of inclusion of data, of publication practices, of the real-world (political) significance of the results. Here we’ve seen presumptions about what is and what is not a "plausible" mechanism to explain variation in IQ testing, and the interpretation of scientific results through the lens of those presumptions. Despite a long history of fruitful investigation into environmental effects, here is where we find the burden of proof being placed such that the tiniest criticism is sufficient for many to dismiss this study and all its implications.

Pinker asks, "Why are empirical questions about how the mind works so weighted down with political and moral and emotional baggage?" I’m not sure I can answer Pinker’s question, but the current research landscape and the reaction this research receives in the larger world suggest that maybe he’s been asking the wrong people.

References Cited:

Duckworth AL, Quinn PD, Lynam DR, Loeber R, & Stouthamer-Loeber M (2011). Role of test motivation in intelligence testing. Proceedings of the National Academy of Sciences of the United States of America, 108 (19), 7716-20 PMID: 21518867

Joseph, J. (2001). Separated Twins and the Genetics of Personality Differences: A Critique The American Journal of Psychology, 114 (1) DOI: 10.2307/1423378

Chiang, M., Barysheva, M., Shattuck, D., Lee, A., Madsen, S., Avedissian, C., Klunder, A., Toga, A., McMahon, K., de Zubicaray, G., Wright, M., Srivastava, A., Balov, N., & Thompson, P. (2009). Genetics of Brain Fiber Architecture and Intellectual Performance Journal of Neuroscience, 29 (7), 2212-2224 DOI: 10.1523/JNEUROSCI.4184-08.2009

Thompson, P., Cannon, T., Narr, K., van Erp, T., Poutanen, V., Huttunen, M., Lönnqvist, J., Standertskjöld-Nordenstam, C., Kaprio, J., Khaledy, M., Dail, R., Zoumalan, C., & Toga, A. (2001). Genetic influences on brain structure Nature Neuroscience, 4 (12), 1253-1258 DOI: 10.1038/nn758

Toga, A., & Thompson, P. (2005). GENETICS OF BRAIN STRUCTURE AND INTELLIGENCE Annual Review of Neuroscience, 28 (1), 1-23 DOI: 10.1146/annurev.neuro.28.061604.135655

About the author: Stephanie Zvan is a science fiction and fantasy writer with a career-stunting dedication to reality. She blogs at Almost Diamonds about whatever strikes her fancy, but her fancy is often struck by the necessary and uncomfortable interesection of science and politics. She also finds it difficult to resist the lure of arguments, particularly those that continually restart from the same points.

The views expressed are those of the author and are not necessarily those of Scientific American.


Comments 27 Comments

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  1. 1. greg_t_laden 10:29 am 05/25/2011

    Excellent analysis and writeup. The null hypothesis is, indeed, that human behavioral and cognitive function develops (and varies) ex-utero mainly in the context of this costly, dangerous, essential and ubiquitous thing we call growing up, in a culture which is being mostly independently transmitted in a somewhat less Darwinian way along side our genomes over time. There is no reason to believe that the outcome (human variation in these things we test and measure sometimes obsessively) is somehow determined by our underlying genome.

    As IQ-mavens are likely to say: "facts are facts even if they are not politically convenient." Well, yeah. And the fact is that our brains vary for reasons other than genetic variation, by and large.

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  2. 2. gcochran 12:01 pm 05/25/2011

    "those political influences in this case aren’t coming from the left"

    I would say that about 98% of them are. In the world I live in, the New York Times is a bigger force, has more readers, has more influence, than Steve Sailer. But only by a factor of 100,000 or so. Now why would someone say that a couple of websites with a tiny readership are the real political influence on this kind of study? That is obviously untrue.

    The null hypothesis is a popular fantasy, nothing more. It could only be true if the human race were born yesterday. Some of us were not.

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  3. 3. Stephanie Z 12:46 pm 05/25/2011

    I’m confused. What does the existence of a generally active or influential political left (to the extent that the Times can even be said to be left) have to do with whether it interferes with or accurately represents the science on this topic? And what does the age of your preconceptions have to do with whether they’re supported by the research?

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  4. 4. byronraum 1:06 pm 05/25/2011

    I am surprised at how some people can still accept the notion that IQ tests measure both motivation and IQ and yet be satisfied at their validity. In order to be so motivation must be always constant. I find it hard to believe they are able to convince themselves that such is the case.

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  5. 5. Jim Lacey 1:12 pm 05/25/2011

    Has anyone investigated highly intelligent individuals who come from modest backgrounds, families that are relatively poor and uneducated?

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  6. 6. greg_t_laden 3:54 pm 05/25/2011

    New York Times = Left? Hahahah!!!

    But seriously, Having lived in Cambridge MA, New York, Minneapolis and the Cozy Hamlet of Coon Rapids, Minnesota, I can verify that where the arguments come from and what they are does vary across the landscape. But that has no bearing on the issue.

    The idea that "the null hypothesis" is some sort of liberal plot is funny … perhaps voltage is a right wing plot? Hypothesis testing? Gravity?

    There may be something missing here … a basic definition of "null hypothesis" is, or at least, how it is meant in this context.

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  7. 7. Susan Silberstein 12:27 am 05/26/2011

    Fascinating. As someone who grew up taking IQ test after IQ test while a parent studied to be a psychologist, I can attest to the role of motivation.

    All science and research is subject to political scrutiny these days; IQ testing has been subject to the whims of political fortune for some years and I’ve been under the impression that it is increasingly used more in industry and less in education.

    I look forward to many more columns from you.

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  8. 8. SohoDiffy 2:20 am 05/26/2011

    Good post, except on the politics surrounding Pinker’s comments. He wasn’t talking about the politics of IQ in the blogosphere: he was referring to the case of a man losing his job for suggesting that there is even a possibility of a link between IQ and gender. I happen to be of the same political bent as the professors who kicked Larry Summers out of Harvard, but you can’t deny that they are to the left of the American public.

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  9. 9. Malev 11:05 am 05/26/2011

    To claim that genetics does not play a role in potential IQ (just as it does for health conditions like diabetes and heart disease) is to completely throw out the theory of natural selection. We can’t pick and choose when natural selection applies and when it doesn’t. Schizophrenia, for example, appears to have a genetic component since indidivudals with family memebers who also exhibit schizophrenia are much mroe likely to experience it themselves. The problem with this topic is that people are too emotionally invested.

    The author cites one researcher who claims malleability and plasticity have no relationship to geentics, but why wouldn’t they? Variability in these traits has been manipulated in animal populations in controlled research settings. If you adhere to evolution via natural selection than any trait that grants an advantage over competitors that leads to more offpsring will become more prevalent in the population due to heritability.

    The author also offer SES correlational data (while throwing out twin study data) as evidence against a genetic factor. IQ varies positively with SES that doesn’t indicate a cuase effect. IQ could cause higher SES (smarter people make more money or obtain better jobs) or higher SES could lead to higher IQ (through more access to resources such as schools). Alternatively there’s a third factor which influences both.

    Environmental factors almost certainly play a role in the development of IQ, as we see in studies on enriched environment, genetically identical populations display more "intelligence" than those raised in meager ones. However "smart" strains of rats can also be bred.

    The author of this article does just as much of damage to IQ research by ignoring genetic factors as those who ignore environmental factors. Whenever the question is nature versus nurture the answer is both. Denying a genetic factor because we don’t like the idea of a pre-determined future does an injustice to this research.

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  10. 10. Malev 11:15 am 05/26/2011

    In addition I’m not sure what qualifies a "science fiction and fantasy writer" as an expert on IQ research.

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  11. 11. Stephanie Z 2:19 pm 05/26/2011

    The only credentials I claim in writing about IQ are being familiar with the literature. Feel free to document specifically where I’m wrong.

    SES is just one significant environmental interaction with IQ. There are quite a number. Are you looking to make a case that all of them (for example, the motivation mentioned in the Duckworth study) are inconclusive on the question of genes vs. environment? Are you prepared to deal with the entire body of even just SES studies?

    Nor do I say there is no connection between genes and IQ. What I said is that people claim that genes account for variability in IQ in the absence of any replicated research that can provide support for the claim. It’s easy to claim that our most plastic organ *must* show some variability controlled by genes, as you do. Backing that up with research has escaped everyone so far, but that doesn’t stop the claims. It certainly hasn’t stopped the pro-genes faction from making accusations of political bias when anyone points out the lack of evidence.

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  12. 12. Stephanie Z 2:27 pm 05/26/2011

    Summers didn’t lose his job over his remarks. He was criticized for poor scholarship. More specifically, he was criticized for speaking at the end of a conference that focused on the environmental effects on differning outcomes between the sexes, and chose to take that opportunity to say, "Nah, to provoke you, I’m going to throw away all that well-established stuff you’ve been talking about for days and say it’s really all about what this study of high school kids tells us is universal to humanity."

    It seems quite appropriate to the topic.

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  13. 13. 3:05 pm 05/26/2011

    Hi Stephanie –
    Thanks for mentioning our studies in your thought-provoking article.
    I do want to clarify 2 things about our studies that you covered:
    1. Our twin studies do not ignore environmental effects –
    we just published the largest-ever diffusion imaging study in twins and showed how specific environmental
    factors (such as SES) do indeed modify the strength and timing of the genetic effect:
    In other words, we are able to detect gene x environment interactions;
    this complements Eric Turkheimer’s findings (which you mentioned) that genetic effects often depend on your circumstances.
    2. You said our twin studies do not look at the genome at all with genetic tests – but we do in fact look at over half a million genotyped SNPs in the twins and other non-twin populations, and we found several genetic variants that affect brain integrity in addition to disease risk – here’s one risk gene that many of us carry (!):
    Thanks for your work, just wanted to clarify these things above.
    - Paul Thompson, Professor of Neurology, UCLA School of Medicine
    ENIGMA Project:

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  14. 14. Stephanie Z 3:40 pm 05/26/2011

    Thanks for the comment, Paul. To clarify for readers, the study you point to in (1) looks at age, sex, IQ, and SEI in relation to the structure of white matter:

    "Subjects’ socioeconomic status was evaluated using the Australian Socioeconomic Index 2006 (AUSEI06; (McMillan et al., 2009)). The socioeconomic index (SEI) is determined using a 0-100 scale based on a person’s occupational category, which may be associated, to some extent, with educational level and income. In our study, SEI was assessed in the adults only, and defined as the higher SEI of their two parents. SEI data were available in 250 families, for a total of 499 subjects, and the median family SEI was 67.5 (25th percentile = 39.7; 75th percentile=83.8)."

    It found, as might be expected from other types of research, significant effects from the environmental variables examined. I would still, however, be interested in your reasoning behind referring to genes and genetic influences in this paper instead of the more certain non-specific "heritability" for those effects not related to the environmental variables your lab studied.

    Again for clarity (since too many people just never follow links), the link you provide in (2) refers to a genetic variant that hasn’t been shown to be a factor in variability in cognition in the absence of Alzheimer’s, although it has been shown to be a risk factor for Alzheimer’s.

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  15. 15. JL 3:46 pm 05/26/2011

    First, thanks for quoting me, Stephanie (third quote from top)!

    Statsquatch’s analysis seems to me to cast serious doubt on Duckworth’s results. The fact that the blogger, a pseudonymous non-psychologist, does not want to publish his analysis as a peer-reviewed comment does not invalidate his conclusions. Nor are, of course, the extensive quotations from Cosma Shalizi in your article invalidated by the fact that they, too, are from a mere blog posting.

    Statsquatch shows that Duckworth’s results are driven by three extreme outlier studies. All three are from the same paper published in 1978, and what’s more, the paper was co-authored by Stephen Breuning who was later caught falsifying research data in some of his other studies. If you remove Breuning’s studies from the meta-analysis, the "motivational effect" is no longer statistically significant. Had a forest plot of the kind Statsquatch created been included in Duckworth’s paper some others might too have been more skeptical towards the study’s results. Of course, we do not know whether those three studies are fraudulent, but the fact that they are extreme outliers in the meta-analysis does raise concerns. For a comparison, none of Cyril Burt’s heritability results have been used in reviews and meta-analyses after some of his results were found to be possibly fraudulent.

    Whatever you think of Statsquatch’s and others’ criticisms and comments, your suggestion that Duckworth’s study "should be eliciting simple head nods" is strange. Voluntarily succumbing to confirmation bias is not conducive to good science. We should be particularly skeptical of results that meet our expectations, although this is admittedly difficult. Scientists are only humans, and peer-review is far from being a watertight process, so I for one welcome the sort of criticisms and reanalyses that you decry in your piece, Stephanie.

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  16. 16. Stephanie Z 3:53 pm 05/26/2011

    Actually, what I’d like to see is a comment from Statsquatch that explains the inconsistency of opinion. The post says there’s a problem, but the comments say there isn’t (not quoted in this post for gratuitous insults): "The paper is OK. It seems plausible that you can incentivize retards to improve a few points on an IQ test. I do not see any big implications, though. If Duckworth is the best anti-IQ warrior they have that side is in more trouble than I thought."

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  17. 17. greg_t_laden 4:25 pm 05/26/2011

    Malev, why? Do you see what you are saying? To make it more clear, and just for fun, lets take a different cognitive behavior: Language. As in, French (not capacity for). If I have the zany idea that which langauge you speak is partly subject to natural selection, and you say no, clearly this is all learned, than is a valid counterargument "To claim that I am wrong is to deny the role of natural selection is clearly wrong because I say it is partly due to natural selection. Therefore it must be."

    I mean, really.

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  18. 18. greg_t_laden 4:31 pm 05/26/2011

    We need to be careful about confusing disease risk and other "broken gene" issues with genes under selection to produce a certain result in the phenotype. Not only is there no viable mechanism for normal human brains varying at the genetic level for traits such as culturally defined intelligence, but there is good reason to suspect, from a biological perspective, that there shouldn’t be. Finding allelic variation that co-varies with what various tests show, in the absence of mechanism of a developmental process that makes a "iq trait" vary is not very convincing that our current nerurological models of how the human cortex develops (primarily through experience) should be thrown out.

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  19. 19. rufusgwarren 7:03 pm 05/26/2011

    Its possible to settle the argument. Build an environment rich with the things that enhance us in a civilised world. Take children from volunteers or orphans with a somewhat defined genetic. Raise the kids within this rich environment and compare the results. Since this environment is to enhance the ability to allow the children to become all that they can be, this will settle the argument. I predict that I/Q will not define a person as a successful citizen but it may demonstrate the ease to be successful citizen.

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  20. 20. denysYeo 7:42 pm 05/26/2011

    I agree, use and promotion of IQ is a political expediency.

    Take one example: IQ scores are predictive (within a range of error) for group data. That is if you take the scores of a group and correlate them with scores on some other variable, such as academic performance, the correlation will be (usually) positive. In other words, performance on the IQ test explains some of the variance on the academic tasks. What a lot of people don’t understand is that if you take one person from this group and try and use their IQ score, to predict their results on the academic tests, the probabilities of getting it right is no better than selecting a number (within the error range) at random.

    Nevertheless, it suits many people (including many psychologists) and groups (such as test companies) to promote the idea that IQ tests can (accurately) predict how an individual will perform in the future in all sorts of areas.

    I have worked as an Educational Psychologist for 20 years; I have never administered an IQ test. I now know that psychologists can do good work without feeling they have to follow the political bandwagons.

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  21. 21. daedalus2u 10:45 pm 05/26/2011

    Stephanie, nice article. It is good to see someone asking for science in the genetics/IQ debate.

    Paul, MZ twins always share an in utero environment as well as sharing a genotype. As I read your paper, you are using a non-standard and idiosyncratic definition of “genetic” and “heredity” as “everything that MZ twins have in common that they don’t share with siblings”. If MZ twins were exposed to alcohol in utero and siblings were not exposed to alcohol (unknown to your reseachers), you would consider the resulting effects of alcohol to be “genetic” because the MZ twins share them.

    Is this interpretation of how you are using the term “genetic” correct?

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  22. 22. statsquatch 11:22 pm 05/26/2011


    Thanks for not linking. I was writing in response to a comment that someone was not going to reference the paper. I think that is an over-reaction. The meta-analysis is sloppy because it does not include a forest plot and they do not mention the heterogeneity in the abstract. However, if you include Breuning (the fraudster) they make a reasonable case that in samples with low IQ you can improve test scores by giving incentives but this is not present in samples with higher IQ. Of course you do not find this in the abstract. I do not know if this fact holds if you exclude Breuning, but if might.

    The second part of the paper is a re-analysis of another study of “at risk” youth that tries to disentangle motivation from intellect as a predictive factor. I have some technical problems with the analyses and the population is not representative but I have seen worse.

    The paper is so carefully written that although, in my view, the authors overstate their conclusion, even with Bruening, they do not do so by much.

    “Collectively, our findings suggest that, under low-stakes research conditions, some individuals try harder than others, and, in this context, test motivation can act as a third-variable confound that inflates estimates of the predictive validity of intelligence for
    life outcomes.”

    Note the soft language: “Collectively” (some of the studies in the meta-analysis and the re-analysis?), “Some invidiuals” (certain low IQ students?) “Suggest” (In some studies?) “can inflate” ( how much?) "life outcomes" (graduation or jail?).

    No, the paper is OK to refernce but you need to read the whole thing including the supporting documents.

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  23. 23. 11:47 pm 05/26/2011

    Thanks Stephanie for your reply. I liked your article and the points you raise are fair and interesting – I don’t think there are any fallacies in
    what you argued. One fair question is "If IQ is genetically influenced, why haven’t people found reliable genetic polymorphisms (common
    variants such as SNPs in the genome) that influence it?". Recently, we found a combination of 4 common SNPs, including the Alzheimer’s risk gene CLU-C, that together account for about 6.7% of the variance in brain integrity in normal young adults, as measured by fractional anisotropy (FA) on diffusion MRI brain scans.
    This hints that they may be genetic variants that affect IQ, as FA correlates with IQ in adults, but only weakly (r^2 around 10-20% locally and less in most parts of the brain). But the correlation is biologically plausible as FA reflects (among other things) myelination and axon conduction velocity, and perhaps also information processing speed in the brain. So if these 4 SNPs jointly explain <0.5% of the variance in IQ, tens of thousands of people with GWAS and DTI scans would be needed to detect and replicate their effect on cognitive function in normal adults. Recent analyses of height show that eventually you may find reliable causal SNPs with massive GWAS meta-analyses (like our Enigma project, which is not about IQ), but they have small effects. So either the heritability is due to (1) exomic variants missed by GWAS, epigenetic or epistatic effects, CNVs, or rare variants, or (2) some confounds masquerading as a gene effect (as some of the other comments here suggest), or (3) a model of gene action that is more mathematically complex than we can build yet, or none of these. Time will tell (and I don’t have any prejudices either way, we are all trying to figure this out).
    - Paul Thompson, Professor of Neurology, UCLA School of Medicine
    ENIGMA Project:

    Link to this
  24. 24. 11:57 pm 05/26/2011

    Daedalus2u – I agree, there are many limitations of classical twin studies (structural equation modeling of MZ and DZ covariances, etc.), and these are hashed out in detail in books by Mike Neale, who wrote Mx, and in many debates about heritability, and in our longer papers where we have space to talk about them (e.g., the review Jeremy Gray and I wrote for Nature Reviews Neuroscience). You are right that there are in utero effects (both shared and nonshared) on members of MZ and DZ pairs, and even some slightly unusual aspects that may slightly differentiate twins from non-twins. By and large the twin design is a useful guide, but we supplement it with other available methods (e.g., candidate genes, GWAS, meta-analysis and replication of SNP effects in non-twin cohorts such as ADNI, etc.).
    Thanks for your comment! – Paul Thompson, Professor of Neurology, UCLA School of Medicine
    ENIGMA Project:

    Link to this
  25. 25. JL 4:31 am 05/27/2011

    Prof. Thompson,

    To avoid some of the possible shortcomings of the twin design, why not use the approach introduced by Peter Visscher and colleagues in their study of the heritability of height? Instead of comparing twins, they compared non-twin siblings by estimating the actual degree of identity-by-descent between them. They found, naturally, that siblings who are more similar genetically are also more similar in height, and their maximum likelihood estimate of the heritability for height was 0.80, which is similar to twin studies. It would be interesting to see a study of the heritability of IQ or brain structure that uses this method.

    Link to Visscher et al. study:

    Link to this
  26. 26. daedalus2u 9:05 am 05/27/2011

    Paul, thanks for your reply, but you didn’t specifically answer my question, which may not have been clear because the quotation marks I used didn’t show up. I will try to rephrase it so it is easier to understand.

    As I read your paper and now your comment, what you are using as the definition of "genetic" is:

    "everything that MZ twins have in common that they don’t share with siblings."

    Using this definition, if MZ twins were exposed to alcohol in utero and siblings were not exposed to alcohol (unknown to your researchers), you would consider the resulting shared effects of alcohol (even to the extent of FAS) to be genetic simply because the MZ twins share them. Is this correct?

    I understand that you think your interpretation of the use of term "genetic" this way is useful, and it may well be common in the literature. I am trying to understand precisely what your data is to then make precise interpretations, not merely useful ones (useful being a subjective term). To me, precision is more useful than saving space with ambiguous and poorly defined terms.

    If you could explicitly give me a precise definition of what you mean when you use the term "genetic" I would appreciate it. Thanks in advance.

    Link to this
  27. 27. logodesign 8:25 am 06/9/2011

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