Variability hypothesis

Two distribution curves with identical means but different variabilities. The curve with the greater variability (green) yields higher values in both the lowest and highest ends of the range.

The variability hypothesis, also known as the greater male variability hypothesis, is the hypothesis that human males generally display greater variability in traits than human females do.

It has often been discussed in relation to human cognitive ability, where some studies appear to show that males are more likely than females to have either very high or very low IQ test scores. In this context, there is controversy over whether such sex-based differences in the variability of intelligence exist, and if so, whether they are caused by genetic differences, environmental conditioning, or a combination of both.