I may be dumb on this - but how do they even calculate this? DEI departments at most companies are not even that old so it would be impossible for someone to b

I may be dumb on this - but how do they even calculate this? DEI departments at most companies are not even that old so it would be impossible for someone to be at their job for 5 years or more. Which would effect the average if it was calculated as a straightforward average. Is it that the median employee last 3 years? With half leaving sooner? Or something else.