Interesting study, lots of numbers and tables. However, numbers don't tell the whole story. Some witnesses (and non-witnesses) upvote for curation, downvote for fighting spam, some have high SP, low SP, this varies the self-upvotes value, some have a lot of whale friends to vote for them, some have less or none, etc... Lots of human factors and politics are at play, not just for witnesses, but for the whole platform. I don't think numbers should be the only factor in determining who to vote for.