The Flynn effect: why IQ norms grow old
For much of the 20th century, each generation did better than the last on reasoning tests. In some countries the rise stopped and turned into a decline, and that changes how a norm has to be built.
In this article
Scores that rose without anyone noticing
An IQ is always a comparison with a reference group, the norm. When a publisher updated a test, it gave the new and old versions to the same people and noticed something curious: everyone did better against the old norm. The reference group from decades earlier had become easy to beat.
The New Zealand political scientist James Flynn pulled these data together. In 1984, he showed continuous gains in the United States between 1932 and 1978; in 1987, he gathered data from 14 countries with the same pattern. The average rise was around 3 points per decade, and the phenomenon came to bear his name.
The size of the gain
In 2015, Jakob Pietschnig and Martin Voracek published a meta-analysis covering a century of data, from 1909 to 2013, adding up millions of participants in dozens of countries. The gains showed up in the total score, on the order of 3 points per decade, and they were larger in fluid reasoning than in crystallized knowledge, such as vocabulary.
The same study found signs of a slowdown in the most recent decades. The rise had not been uniform over time, and in several places it seemed to be losing steam.
What might explain it
A change of 3 points per decade is far too fast to have a genetic cause. The explanations under discussion are environmental, and several of them likely act together.
- Schooling: more people studying for more years, in schools that train you to classify, abstract and work with hypotheses.
- Nutrition and health: over the same period, average height and childhood health also improved in many countries.
- Cognitive environment: Flynn argued that the 20th century taught people to think in abstract categories, the kind of thinking tests demand.
- Smaller families and more attention per child, along with greater familiarity with exams and forms.
There is no consensus on the weight of each factor, and the debate remains open.
The reversal in some countries
Norway has tested the reasoning of men called up for military service since the mid-20th century, using the same type of test. Bernt Bratsberg and Ole Rogeberg (2018) analyzed more than 700,000 results from men born between 1962 and 1991. Scores rose until the generations born in the mid-1970s and then began to fall.
The study's strongest point was comparing brothers. The decline also appears within the same families, between the older and the younger brother. That rules out the explanation that the average fell because the profile of who has children changed, and points to environmental causes. What those causes are, the study doesn't say. Reports of stagnation or decline have also come from other Nordic countries.
Why this forces norms to be redone
A norm is a snapshot of the population at one moment. If average performance shifts about 3 points per decade, a norm from twenty years ago may be off by about 6 points. With the old norm, a generation that rose looks above average without being so; for a generation that fell, the error goes the other way.
That's why the major batteries are renormed from time to time, with new samples. A result only makes sense together with information about which norm was used and when it was built.
Every norm has an expiration date. An honest test tells you which norm it used.
What this has to do with IQNorth's norm
IQNorth's norm is provisional, and the Flynn effect is one of the reasons to say so out loud. It uses published ICAR parameters, corrected because people who take part in online research score higher than the population, and the age curve from the literature (Salthouse, 2009). It will be recalculated with the real responses of people who take the test, separately for each language, and the report always states which norm was used. The step-by-step is in the method.
See also: The method.
Sources
- Flynn, J. R. (1984). The mean IQ of Americans: Massive gains 1932 to 1978. Psychological Bulletin, 95(1), 29–51.
- Flynn, J. R. (1987). Massive IQ gains in 14 nations: What IQ tests really measure. Psychological Bulletin, 101(2), 171–191.
- Flynn, J. R. (2007). What Is Intelligence? Beyond the Flynn Effect. Cambridge: Cambridge University Press.
- Pietschnig, J., & Voracek, M. (2015). One century of global IQ gains: A formal meta-analysis of the Flynn effect (1909–2013). Perspectives on Psychological Science, 10(3), 282–306.
- Bratsberg, B., & Rogeberg, O. (2018). Flynn effect and its reversal are both environmentally caused. Proceedings of the National Academy of Sciences, 115(26), 6674–6678.
