The "Flynn effect" is the substantial and long-sustained increase in intelligence test scores measured in many parts of the world. When intelligence quotient (IQ) tests are initially standardised 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 IQ points. When IQ tests are revised they are again standardised 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 Flynn effect is the subject of a multiple-author monograph published by the American Psychological Association in 1998.