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China AirPollution2

News has come in from China that air pollution has a large and cumulatively damaging effect on intelligence, particularly on older people with less education. Perplexingly, the effect is on Vocabulary, but not Maths. Even more specifically, the verbal decrement hits men harder than women. What is going on? How could bad air have such a specific effect, and all this within a mere 3 years?

In terms of the wider debate about whether intelligence tests mean anything, does this prove that intelligence tests actually test intelligence, or does it mean that they only test intelligence when measuring pollution, but not when they test differences between one person and another, or one group and another? Perplexing stuff. Odd that some critics who doubt that people can be validly tested for intelligence have no doubt about intelligence when the effect of a pollutant is identified.

However, in many eyes this paper about a pollution effect on intelligence proves the case for bicycles and the banning of diesels, or cars generally.

This would not be the first time that researchers have found that pollution damages the mind.

Those researchers found that for each 5ug/dl exposure at age 11 overall IQ dropped by 1.61 points. The effect on perceptual reasoning was a bit higher, the effect on working memory a bit lower, and nothing much on verbal comprehension.

What have the new researchers found?

The impact of exposure to air pollution on cognitive performance
Xin Zhanga, Xi Chenb, and Xiaobo Zhang

The paper is detailed, and carefully argued. Population sampling is very good. They studied sulphur dioxide, nitrogen oxide and particulates (PM10).

chinese pollution figures

A 1 SD increase in average API (exposure to pollution) over 3 years before the interview is associated with 1.132 points (0.108 SD) drop in verbal test scores.

Air pollution has a stronger effect on white matter (required more by verbal tests) than on gray matter (required more by math tests). Since men have a much smaller amount of white matter activated during intelligence tests, their cognitive performance, especially in the verbal domain, tends to be more affected by exposure to air pollution.

I am not sure why the response to overall pollution is so specific. It just seems odd. I am also not sure about the proffered explanation for the sex difference. It is based on a finding from Haier 2005 about white and grey matter activation in doing verbal and mathematical tasks. Anyway, they say it is a future research topic.

The scoring system is not the total number of items correct, but the highest rank of question achieved. This might introduce artefacts if the items are not perfectly ranked. It might also cause problems if the ranking of maths problems is easier to achieve than the rankings of word recognition. The test starts at different points according to the completed school stage of the participants. So, it is targeted at ability levels, and may be a little less reliable than a full test, but this is probably a minor issue. They control for family income and years of education, which will reduce individual variation in scores because such “corrections” assume that neither variables are caused by intelligence. They tested 25,486 respondents from the national sample, so perfectly good for this study. They omitted the 1.3% of subjects who had moved from one part of the country to the other (though with more time it would have been interesting to see if their results were affected by moving to more or less polluted places). They excluded those with very polluted occupations.

The population-weighted annual mean concentration of PM10 over 2014 in China is 112 μ g/m3, much higher than the National Ambient Air Quality Standards (NAAQS) published by the U.S. Environmental Protection Agency (EPA). This is a very important point in the supplementary materials, which in my view would have been better placed in the body of the main text. I could not find tables showing the effects for cities versus the countryside, which would have been informative.

It is good to see intelligence testing being used in this work. The results are interesting and quite alarming. However, it is hard to see how they could be having the particular reported effects on Vocabulary and not Maths, and for men more than women. If the very high level of pollution in China is having a massive impact then I would expect that no person or ability would remain unaffected. If pollution in 3 years is having such a big effect, even on Vocabulary alone, it is a puzzle that intellectual and scholastic achievement tests in China do not appear to reveal this effect, and regularly come well above Western achievements. The effect of pollution on intelligence is worth further investigation.

• Category: Science • Tags: China, Pollution 
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  1. In terms of the wider debate about whether intelligence tests mean anything, does this prove that intelligence tests actually test intelligence, or does it mean that they only test intelligence when measuring pollution, but not when they test differences between one person and another, or one group and another? Perplexing stuff

    It’s not in (((weshtern))) but in Tchaina…

  2. Yee says:

    For the last 3 years, Chinese people also gain more weight, spend more time on smartphones, have higher income, more people convert to Christianity and Islam, women wear shorter skirts, use more cosmetics… Any study on whether those lower our IQ score?

    I suspect more people convert to Christianity and Islam is the culprit…. Sure doesn’t need intelligence for that.

  3. Sean says:

    Do articulate and intelligent people and their kids live better and in nicer locations? If intelligent people live in less polluted places it is difficult to see a real causal relationship.

    The levels at which potentially toxic substances such as mercury and lead are classified as dangerous may have been miscalculated, two US scientists are warning. Risk assessments and regulations on safe limits for these substances in medicine and the environment may have to be rethought, they warn1. There are safe levels below which potential pollutants and poisons may actually be beneficial, say Edward Calabrese and Linda Baldwin of the University of Massachusetts in Amherst. For the past 30 years, cancer-causing chemicals and X-rays have been viewed largely as dangerous whatever their level. “The field of toxicology has made a terrible blunder,” says Calabrese. “A lot of high-powered people need to take the time to explore this.” For example, dioxins, which are industrial by-products that at certain doses can cause cancer, can actually reduce tumour growth in some species. Similarly, small amounts of the toxic trace metal cadmium can promote plant growth. “What we call ‘toxic chemicals’ is a misnomer,” says cell biologist and UK government advisor Anthony Trewavas from Edinburgh University. “Mild chemical stress is beneficial.”

  4. @dearieme

    Small sample size, but could be on to something if proper psychometrics were to be applied. I assume many journalists are bright, but always in a hurry, and with a flair for the captivating metaphor. A talent, but not a source of reliable knowledge.

    • Replies: @pyrrhus
  5. Columbia University seems to release a study every year or two about the effects of pollution on children. In 2015, the school’s study said that a combination of pollution and poverty lowers a child’s IQ. I read the study which also stated that children who only experienced one hazard, either pollution or poverty, had higher group IQs than the children who did not experience pollution nor poverty. So the children who should have had the highest IQ placed third out of four groups.

    • Replies: @James Thompson
    , @res
  6. @Triumph104

    Seems they were able to show an effect of pollution, but the attempt to link lowered intelligence to poverty is genetically confounded.

  7. pyrrhus says:
    @James Thompson

    Probably wrong assumption, Dr. Thompson…Based on the people we see graduating from Journalism schools in the US, journalists are almost as dumb as Education majors, who are rock bottom of the legitimate majors. (I exclude fake majors and courses created for scholarship athletes.)

  8. Anon[381] • Disclaimer says:

    But what were the maths that were tested/examined???

    The level of math tested could have been ‘no brainer’ math!

    And likewise, what was the level of vocabulary tested? It could have been obscure, abstract language of some esoteric field, that the test subjects were not in their own field.

  9. Jorge Videla [AKA "jorge raphael videla"] says:

    and regularly come well above Western achievements

    only for the select subpopulation of city dwellers. IQs in the countryside are lower than those for american negroes. i presume pollution is worse in the cities.

    Odd that some critics who doubt that people can be validly tested for intelligence have no doubt about intelligence when the effect of a pollutant is identified.

    the same is true of those who claim black africa’s IQs are depressed by disease and malnutrition.

    IQ tests are the single best operationalization of “intelligence” and correspond to subjective assessments well enough. it’s a pity that the IQ “experts” don’t understand this and think of intelligence as a thing. but psychology professors have low IQs. so no surprise.

    you’re welcome.

  10. res says:

    There is a version of that paper available at

    I’m not sure what to make of it. The sample size is not that large (~200), they used imputation for missing variables, and they did not perform Bonferroni adjustment (or similar) to account for their testing of multiple hypotheses.

    I suspect Dr. Thompson is right about a genetic confound. Though Table 2 indicates: “Adjusting for ETS, sex, maternal education, maternal intelligence, ethnicity, and the home caretaking environment.” Not sure if this matters:

    There were no significant differences between the children included in the analysis and those not included due to missing WISC outcome or cord adduct data (n=118), except that there was a higher percentage of African Americans in the included group (38% vs. 26%) (Supplemental Table S1).

    Does anyone know how to convert the TONI scores they used to measure maternal IQ? The closest I see is this image which equates a 22 to a 98 IQ for an 11 year old. The paper gives mean/SD/range of 20.7 8.7 (0, 43)

    I assume the relative group ordering you give is based on Figure 2. I think the error bars there indicate that ordering should be taken with a grain of salt.

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