Liking a post is actually rating it "100", disliking a post is rating it "0". The rating is sort of the average of these scores, although weighted based on the total number of ratings (so the first few ratings can't cause wild swings). Liking/disliking also feeds into the popularity or controversiality of a post. In short, like/dislikes are inputs into the system, but they're not designed to be viewed as aggregates themselves.