Ratings: So i'm curious about IMDb ratings on TV shows

When you see a tv show like "Teen Wolf" "Supernatural" "Game of Thrones" "The big bang theory" and an endless list of different TV shows. They all have their ratings, all different. Some is at a very good rating and some is at a lower rating. My question is, and sort of idea if this isn't a thing already. How does the shows get rated, do they simply get rated by people who rate it at their IMDB page? If so thats a bad way to rate a tv show. A person usually rates the tv show based on the first episodes or season, if the first season is not great, he'll maybe give a 5 or a 7 or whatever. But the show has lets say 6 epic seasons after the first one, all episodes gets great ratings. What IMDB should do would be to give the show page a rating which is calculated over all the episodes ratings together, making the rating average over all the episodes, rather than someone rating the show bad or worse than it is cause it had a couple of bad first episodes or season. That may make several people strive away from watching the show cause it had a bad IMDB rating cause the first episodes / season was bad. If IMDB doesn't already average the shows rating based on all the episodes ratings, thats really something they should do. So this is an idea, but also a question.