[marcinzm]

Your comment doesn't change if you replace lines of code with manager's perception of you. If you're both equally liked by your manager then you should receive the same rating. Within the metric being defined neither is biased since they have clear and explicit definitions. Against the true metric of "productive engineer" both are biased.

[qbasic_forever]

And how do you handle your manager having a cultural or unconscious bias against your <race / religion / body type / gender / appearance / clothing / hair color / fragrance of the soap you use / eyewear / etc.>? You just live with them not liking you and not measuring up to others in their mind?

[closeparen]

Subjective evaluation for performance purposes is often done by committee for this reason. Your work is read by several people who are unlikely to have the same idiosyncratic biases, at least some of whom don't know you. (That cuts both ways, though; they also don't know the context for the work).

[giantg2]

Except you have no measure or target for the manager's feelings.

You have to define productive engineer in order to claim the metrics are biased.