I understand that by definition, the mean IQ is 100. And that over time IQ tests are updated to ensure that mean remains 100.
But if IQ scores were not updated, what would mean IQ be now and how has IQ changed over time?
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Until recently, when people took older tests, they tended to score higher.
The Flynn effect is the substantial and long-sustained increase in both fluid and crystallized intelligence test scores that were measured in many parts of the world over the 20th century. When intelligence quotient (IQ) tests are initially standardized using a sample of test-takers, by convention the average of the test results is set to 100 and their standard deviation is set to 15 or 16 IQ points. When IQ tests are revised, they are again standardized using a new sample of test-takers, usually born more recently than the first. Again, the average result is set to 100. However, when the new test subjects take the older tests, in almost every case their average scores are significantly above 100.
The recent years saw a reversal of the Flynn effect.