I worked at a large enterprise software company and it was actually fairly easy to tell. The reason is that management had implemented a Scrum system with two-week sprints. What this meant is that we planned out what we could do for the next two weeks on the first day of the sprint, including doing estimates of the tasks. Then at the end of the week we would look back and double check that we got everything done and try to figure out why we were off if were (but they never figured it out).
When doing group estimates, it's not hard to start to see who is struggling to finish their tasks at the end of the week and who is finishing with time to spare. You can also tell who is giving QA headaches with all their bugs and who is saving QA time. A lot of the people didn't realize they were doing it, but you could tell QA would base their estimates partially on who was going to be on the coding portion, and it was very easy to get a sense of who was able to get tasks done faster than you thought you would be able to and who was slower.
The worst was the programmers that needed the other programmers to help them out almost every sprint. Management liked it. They said it was a good sign because it showed what a team we were.
When doing group estimates, it's not hard to start to see who is struggling to finish their tasks at the end of the week and who is finishing with time to spare. You can also tell who is giving QA headaches with all their bugs and who is saving QA time. A lot of the people didn't realize they were doing it, but you could tell QA would base their estimates partially on who was going to be on the coding portion, and it was very easy to get a sense of who was able to get tasks done faster than you thought you would be able to and who was slower.
The worst was the programmers that needed the other programmers to help them out almost every sprint. Management liked it. They said it was a good sign because it showed what a team we were.