If someone really does nothing, it's really obvious. You don't need statistical analysis to determine who it is, just ask their teammates. Developers don't work in isolation. Actually, it's a very collaborative job where you're in constant interaction with other people. If someone doesn't contribute their fair share, it's going to be obvious very quickly.

The problem is often a lack of mechanism to act on it. Sure everyone might complain about a coworker, but once a person is hired they become just a number and management doesn't typically care about individual performance, only that all the spots in the org chart are filled.