As David Blanchflower wrote in this week's economics column:
The gap between mean and median self-employed earnings is greater than for employees, because their mean is pulled up by small numbers of highly paid individuals who earn many millions. But the typical self-employed person earns much less than the typical employee. Moreover, the earnings of the typical self-employed person have fallen in nominal terms, while median employee earnings have risen by nearly a third. The reason why mean self-employed earnings have risen (while median earnings have fallen) is that self-employed earnings at the top have risen by a lot. We are not all in this together.