Is the Flynn effect related to migration? Meta-analytic evidence for correlates of stagnation and reversal of generational IQ test score changes

Generational IQ test score gains in the general population (the Flynn effect) have been observed to diminish in strength in recent years, and there is evidence for a stagnation and even a reversal of the Flynn effect in a number of countries. Here, we show that there is only little evidence for effects of migration, fertility, and mortality as substantive correlates of IQ decreases. We argue that the stagnation of the Flynn effect may be explained by ceiling effects and diminishing returns of IQ-boosting factors, whilst its reversal can be attributed to negative associations with psychometric g.