What intelligence researchers think about heritability


I discussed this survey of intelligence researchers in December 2013



Asked: Is there sufficient evidence to arrive at a reasonable estimate of the
heritability of intelligence in populations of developed countries?” 73% said Yes.

Asked: What are the sources of U.S. black-white differences in IQ?

0% of differences due to genes: (17% of our experts)
0-40% of differences due to genes: 42% of our experts
50% of differences due to genes: 18% of our experts
60-100% of differences due to genes: 39% of our experts
100% of differences due to genes: (5% of our experts)
M=47% of differences due to genes (SD=31%)

Now we have the first publication on this survey:

Survey of Expert Opinion on Intelligence: Causes of International Differences in Cognitive Ability Tests Heiner Rindermann David Becker and Thomas R. Coyle

Intelligence March 2016 | Volume 7 | Article 39 


Following Snyderman and Rothman(1987,1988), we surveyed expert opinions on the current state of intelligence research. This report examines expert opinions on causes of international differences in student assessment and psychometric IQ test results. Experts were surveyed about the importance of culture, genes, education(quantity and quality), wealth, health, geography, climate, politics, modernization, sampling error, test knowledge, discrimination, test bias, and migration.The importance of these factors was evaluated for diverse countries, regions, and groups including Finland, East Asia, sub-Saharan Africa, Southern Europe, the Arabian-Muslim world, Latin America, Israel, Jews in the West, Roma (gypsies), and Muslim immigrants. Education was rated by N=71 experts as the most important cause of international ability differences. Genes were rated as the second most relevant factor but also had the highest variability in ratings. Culture, health, wealth, modernization, and politics were the next most important factors, whereas other factors such as geography, climate, test bias, and sampling error were less important. The paper concludes with a discussion of limitations of the survey (e.g.,response rates and validity of expert opinions).

Differences between countries with the lowest and highest ability levels are large. For example, in TIMSS 2011, 4th grade Yemeni pupils achieved 209 student assessment study (SAS) points, whereas South Korean pupils achieved 587 SAS points. If SAS points are converted to IQ points, the Yemeni would have an IQ of 56 and the Koreans would have an IQ of 113, a difference of 11 years of schooling. Psychometric IQ studies show similar results. For example, Malawi has an estimated IQ of 60, whereas Singapore and Hong Kong have estimated IQs around 108, a difference that translates into SAS≈233 and 555 or 16 years of schooling.

When authors give ability differences as “years of schooling” this always provokes the response that countries with lower levels of ability need more schooling. It really means “despite schooling, as if they permanently required 16 more years of schooling”. The main reason that intelligence is not a popular subject is that it has been shown not to be very malleable. At a rough estimate, anyone of IQ 93 and below finds it difficult to earn good wages.

The authors explain that: the conversion transforms the SAS-scale (M = 500, SD = 100) in developed countries to an IQ scale (M = 100, SD = 15). We assumed an increase of 35 SAS points, or 3 IQ points per year of schooling (Winship and Korenman, 1997; Rindermann, 2011).

In the current study, data collection procedures were designed to ensure anonymity. The anonymity was implemented to reduce pressure for socially desirable responses, and to increase the likelihood of obtaining honest opinions. Opinions made in anonymity (without fear of retribution) may differ from public appraisals such as those reported in Gottfredson’s (1994) “Mainstream Science on Intelligence,” which was signed by more than 50 researchers.



Notice of the study was emailed to experts who published articles on or after 2010 in journals on intelligence, cognitive abilities, and student achievement. The journals included Intelligence, Cognitive Psychology, Contemporary Educational Psychology, New Ideas in Psychology, and Learning and Individual Differences. Notice of the study was also emailed to members of the International Society for Intelligence Research (ISIR), and posted to the web site for the International Society for the Study of Individual Differences (ISSID). ISIR and ISSID support intelligence research and host professional conferences with intelligence researchers. Finally, the study was announced at the 2013 ISIR conference in Melbourne, Australia. A total of 1345 people received an email invitation. An expert was defined as a person who had published on cognitive ability or who had attended intelligence conferences and presented research. Compared to Snyderman and Rothman (1988, pp. 46–49), our selection criteria were based more on publications in specific scientific journals and less on membership in scientific organizations. In addition, we used email and a web based survey rather than traditional mail and paper-pencil surveys.

The low response rates may be attributed to the length of the survey (which took about 40–90 min to complete), self-censorship, or fear of addressing a controversial subject (despite assurances of anonymity). The low response rates may also reflect a paucity of experts on intelligence and international differences in cognitive ability. There may be 20–50 scientists who study international differences in intelligence. Based on this estimate, the number of respondents (71 people) may exceed the number of scientists who study the topic!

Speaking personally, I found the survey too long, and too interested in subtle points of distinction between various ways of describing intelligence. However, I am easily bored.

Around 90% of experts believed that genes had at least some influence on cross-national differences in cognitive ability.

National IQ causes

As you can see, experts back genes, education quality and quantity, culture and health, plus a scattering of other causes as being the reasons for national differences in ability.

Assuming that the survey is representative of expert opinions, genetic factors should receive more attention in future research and public debates. To fairly consider different hypotheses, future research should incorporate procedures (e.g., rules for methods of argumentation) that reduce zeitgeist or political pressures that may bias responses on controversial issues (e.g., Segerstråle, 2000; Jussim et al., 2015).

Education was measured with two items, environmental factors with 11 items, and genetics with one item. To better estimate the importance of nature and nurture, a single binary question could be added to future surveys (e.g., “Which is more influential, genetic or environmental factors?”).

A single empirical study can contradict expert opinion, and the results of the current survey must be validated in future empirical research.

This last observation is crucial. Expert opinion is no more than an indication of the current state of the argument among informed persons. A new discovery can change the argument. More genetic research, particularly on racial differences on intelligence (which as far as I know has never been funded) would be very likely to strengthen the genetic interpretation, but a negative result would be very interesting. Solid proof of environmental manipulations and educational techniques to overcome national and racial differences in intelligence would swing the argument in favour of environmental explanations.

Perhaps we should predict what such a survey will find by 31 December 2020. I assume there will be no funding for such research, and that results will have to be obtained by making assumptions about censored data. I am not a super-forecaster, but I think that genetic explanations for national and racial differences in intelligence, as shown in Table 1, will rise from 20% to 30% but the standard deviation will remain just as large.  

What are your precise predictions?

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