There seem to be two large possible sources of bias, that is, things which could cause different voting on identical answers:
we could be more likely to upvote answers for high-rep users, especially ones with familiar names
we could be more likely to upvote answers with high scores, and downvote answers with low (negative) scores (even assuming that all answers fit on the screen)
Of course, high-rep users are generally likely to write answers worth upvoting, and high-scoring answers are often worth a vote. But humans are not generally perfectly rational; I assume there is bias. Have there ever been attempts to quantify the effect here? (Please try to avoid answers based on opinion and anecdote.)
Edit: I tried to write this as neutrally as possible. I am not arguing that Stack Exchange is fundamentally broken, or that you personally are a biased voter and therefore a bad person. I am not complaining about any perceived unfair voting. I think high-reputation users deserve their reputation. I like these sites. I'm just curious, within this context, how large of an effect cognitive biases have.
Another edit: I'm curious about the downvoting. I know it's different on meta, and I'm not offended, but since the core idea of the question is "is there any data about this effect" I'm wondering how people disagree - simply because it's hard to measure, or you believe that it would be bad for us to even know the answer? I'm happy to try to improve the question.