A few years back I worked with two engineers who sat side by side, over the course of a month the one girl fixed one bug, while the guy next to him did 22. Having worked with them both I believe they were actually about equal despite the numbers. The girl randomly drew a complex bug that was hard to figure out, while the guy got a bunch of easy ones (including one the is not spelled t-e-h)

This variance is why it is so hard to assign objective numbers.