I think this is were good managers come in. I don't think we have good enough theories in place at the moment to rank people based on algorithms. I've seen people trying to rank software on algorithms and it is extremely inferior compared to the judgement of an experienced individual.

I think for people you need to be flexible and keep the human element.

This is the kind of thing that needs to be done by Watson like computers and needs lots and lots of research.

By all means collect metrics but bad managers may use such applications too literally.