From reading Intelligence, subtitle All That Matters. Stuart Ritchie. McGraw-Hill, 2015. ISBN 9 781444 791877
In the 1960s, the Norwegian government (p 92) decided to add two extra years to the mandatory curriculum for all pupils.Two additional pieces of good luck allowed researches, who came on the scene much later, to turn this into a test of the effects of schooling on IQ.
- First, the reform was implemented across the different parts of Norway in a staggered way – it happened in some areas years before it happened in others
- Second, every male Norwegian sits an IQ test as part of their compulsory army service.
In 2012 the researchers were able to compare the later IQ scores of those who had been forced to stay in school for extra years with the scores of those who hadn’t (Brinch and Galloway, 2012).
1 Year Extra School, Increased IQ by 3.7 Points
They worked out that the extra schooling added 3.7 IQ points per year.
This confirmed the results of many other, previous studies that hadn’t used such elegant methods.
Psychometricians, those that focus on measurement of intelligence via IQ, routinely adjust the mean of test scores to maintain the IQ average of 100, yet it remains true that the ability of people to solve intelligence questions continues to grow.
Other Noteworthy Points
Heritability (p 67). Fifty percent heritability doesn’t mean that 50% of an individual person’s intelligence is due to their DNA. It describes the reasons for variation among the people being studied.
- Heritability doesn’t tell us anything about the average level of intelligence. Intelligence can be 50% heritable in a group where the average IQ is 85, 100, or 115, or an other number
- ‘Heritable’ doesn’t mean the same thing as ‘hereditary’. These words are often confused: a ‘hereditary’ trait is simply anything that’s passed on from parents to offspring, whereas ‘heritability’ is about the genetic variation in that trait.
Flynn Effect (p 94-99). IQs have been increasing about 3 points every decade since IQ testing began.
- Ritchie mentions the interesting hypothesis that the cause may be cultural – we think more abstractly than our ancestors, not faster. Speculatively, we relate knowledge to how it is taught, not how it is experienced.
- For example, a hundred years ago the answer of what do dogs and horses have in common was they are both are used to hunt (a relationship a person has seen). Now the answer is more likely they are both are mammals (a taught distinction).