New study on the Flynn-effect shows possible explanations, why does our IQ rise?

If you don’t know the Flynn-effect, this is a short Wikipedia definition:

…the substantial and long-sustained increase in both fluid and crystallized intelligence test scores measured in many parts of the world from roughly 1930 to the present day.

Many reasons have been discusses why this happen, e.g. Steven Johnson sees a link with popular culture or Flynn links it with education or even lead.

Now there is this study who looked at 100 years of IQ-tests in 31 countries worldwide and with some very interesting insights.

  • “…there is little doubt that education plays a role in explaining the Flynn effect. Nonetheless, schooling is unlikely to account for the full extent of the IQ gains, and in particular the large gains for fluid IQ cannot be attributed to better education.”
  • Technology as a factor for the rise of IQ can not be dismissed, but “…there is no conclusive evidence for increased fluid task performance of individuals that are habitually more frequently exposed to visual media.” The study also mentions e.g. Kenya who saw a rise of IQ despite having limited access to ICT.
  • “… the present findings render it quite unlikely that effects of decreasing family size are substantially contributing to IQ gains.”
  • On the possible explanation that our IQ has risen because we want to guess more: “Decreasing IQ gains in more recent years might be an expression of a beginning saturation of guessing-related gains. Moreover, the considerable crystallized IQ gains in our data would be difficult to be explained by guessing behavior alone, as the majority of crystallized IQ measures in the present investigation were knowledge-based tests that leave only little room for guessing.”
  •  On lead: “A direct assessment of effects of lead on IQ gains was not possible in our meta-analysis, because blood lead–level reports were unavailable or largely incomplete for several of the included countries. However, the above evidence indicates that reduced lead exposure may well account for a portion of IQ gains in more recent years.”
  • Genes maybe?: “Although genomic imprinting in principle would be suitable to explain IQ gains, this hypothesis remains difficult to test. Although influences of genomic imprinting cannot be completely ruled out, in the light of the observed fluctuations in the slope of IQ test score gains over time, this mechanism appears to be insufficient to plausibly explain the observed pattern in our data.”
  • Nutrition? “If improved nutrition were the sole cause of IQ gains, we would expect to observe more or less identical IQ gains at any age starting from infancy. Indeed, we observed nontrivial gains for children samples, thus suggesting an important role of nutrition for the Flynn effect. However, in our data, adults showed substantially stronger gains than children and adolescents. Stronger IQ gains of adults suggest meaningful effects of further causes that emerge only later in development.”
  • On stress: “Similar to improved nutrition, reduced pathogen stress would be suitable to explain stronger fluid than crystallized IQ gains and would be expected to emerge in infancy. Again, the observed stronger gains for adults than for children and adolescents would be difficult to reconcile by this theory, thus suggesting other important factors contributing to the Flynn effect. However, effects of nutrition and pathogen stress remain difficult to disentangle in the context of the present research.”

But in fact it’s probably a combination of these factors who are to ‘blame’. In short:

There may be several contributing factors to this ubiquitous but apparently decelerating effect. The totality of retrievable empirical evidence on this phenomenon, as quantitatively summarized here, points toward components of life history speed, such as improvements of education and nutritional factors as well as a reduction of pathogen-related factors, as the prime candidate causes of the Flynn effect, whereas differences in the strength of gains between intelligence domains may be accounted for by social multipliers (societal IQ increases that may act as IQ-increasing factors in their own right) and economic prosperity.

From the press release:

Now, researchers of the University of Vienna provide the largest account of IQ gains so far: Based on data of almost four million participants from 31 different countries, they were able to show that IQ increases amounted to about three IQ points per decade over a period of more than 100 years (1909-2013). Interestingly, global increases could be observed for reasoning as well as knowledge, although reasoning increases were substantially larger.

Based on this large data set and differences in strengths of gains over time and in different IQ domains, it was possible to evaluate potential causes of the Flynn effect: Improved nutrition, hygiene and availability of medical services which benefit foremost child development, as well as better education emerged as prime candidates for gains.

IQ test standardization

IQ tests are standardized to an average IQ of 100 and an average deviation of 15 and test results follow a bell-shaped curve. Many naturally measurable variables follow such a bell-shaped curve. This means that two out of three people score between 85 and 115 and 96 out of 100 between 70 and 130 IQ points. To account for changes of population ability, IQ tests are routinely reset to a quota of 100.

As mentioned above, the study results showed an average increase of about three IQ points every ten years. But do these results mean that an average IQ test result of 100 points in the present day would translate into an IQ of 130 a century ago? Although gains of about 30 points over a hundred years might suggest so, such an interpretation seems unlikely. Rather than increases in general cognitive ability, these gains are more likely to reflect improvements in specific abilities. “A person with an average IQ score of 100 in the early 20st century might have had quite different capabilities than a person with a seemingly equivalent IQ score of 70 in the present day”, explain Jakob Pietschnig and Martin Voracek of the University of Vienna. IQ gains thus appear to be hollow in terms of global cognitive ability changes. Higher IQ test scores are more likely reflective of increasing specialization and better test taking strategies of participants.

Periodic changes

Interestingly, the strength of gains appeared to be non-linear. This means that periods of rather strong gains alternated with periods of smaller gains. For instance, periodic changes revealed smaller gains during the time of World War II in Europe, a time of considerable environmental stress.

Although IQ gains appear to be still ongoing, study findings suggest that the strength of gains has been substantially decreasing in the recent decades. This may indicate that beneficial effects of factors improving our test scores have peaked and IQ increases might cease in the coming decades. Future research will show whether these observed decelerations of the IQ gains will lead to an end or ultimately a reversal of the Flynn effect.

People like Nicholas Carr or Manfred Spitzer blame technology for the deceleration, but maybe it’s because of rising augmented environmental stress, or because the causes why it augmented in the first place have now become common place for many?

Abstract of the study:

 The Flynn effect (rising intelligence test performance in the general population over time and generations) varies enigmatically across countries and intelligence domains; its substantive meaning and causes remain elusive. This first formal meta-analysis on the topic revealed worldwide IQ gains across more than one century (1909–2013), based on 271 independent samples, totaling almost 4 million participants, from 31 countries. Key findings include that IQ gains vary according to domain (estimated 0.41, 0.30, 0.28, and 0.21 IQ points annually for fluid, spatial, full-scale, and crystallized IQ test performance, respectively), are stronger for adults than children, and have decreased in more recent decades. Altogether, these findings narrow down proposed theories and candidate factors presumably accounting for the Flynn effect. Factors associated with life history speed seem mainly responsible for the Flynn effect’s general trajectory, whereas favorable social multiplier effects and effects related to economic prosperity appear to be responsible for observed differences of the Flynn effect across intelligence domains.

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