Flynn Effect is the phenomenon in which there is a marked increase in intelligence test score averages over time. It is supported by the fact that these increases are large on intelligence subtests that focus on abstract thinking, while the gains on traditional subjects such as vocabulary and mathematics have been very small. This effect of an apparent increase in IQ has also been observed in various other parts of the world, though the rates of increase vary. There are many possible explanations for the Flynn Effect including better nutrition, less infectious disease, longer and more productive education, and more stimulating environments.