You have to click through to discover that though, and there are exceptions who have a low ratio but don’t need downvotes explained to them. (I don’t know if there are such users with a low ratio and low total, though.)
You can see a comment’s karma ratio by hovering on the comment’s karma, but to see the user’s ratio you need to click through to the user’s page and hover over their karma there.
You can detect newbies by their low karma and moderate positive ratio. The registration age doesn’t mean much really.
You have to click through to discover that though, and there are exceptions who have a low ratio but don’t need downvotes explained to them. (I don’t know if there are such users with a low ratio and low total, though.)
You can see the ration in the tool tip over the karma.
Interestingly there are users with positive ratios arbitrarily close to 50%.
You can see a comment’s karma ratio by hovering on the comment’s karma, but to see the user’s ratio you need to click through to the user’s page and hover over their karma there.