The heritability of IQ measures the extent to which the IQ of children appears to be influenced by the IQ of parents. Because the heritability of IQ is less than 100%, the IQ of children tends to "regress" towards the mean IQ of the population. That is, high IQ parents tend to have children who are less bright than their parents, whereas low IQ parents tend to have children who are brighter than their parents. The effect can be quantified by the equation where
- is the predicted average IQ of the children
- is the mean IQ of the population to which the parents belong
- h² is the heritability of IQ
- m and f are the IQs of the mother and father, respectively.
Thus, if the heritability of IQ is 50%, a couple with an average IQ of 120 may have children that average around an IQ of 110, assuming that both parents come from a population with a median IQ of 100.