The Index is heavily influenced by availability. Citizen Kane is essential viewing for film students. Shawshank is essential viewing because it is on cable television every Sunday afternoon and has been on Netflix/library shelves for a decade. Because more people have seen it recently, more people vote on it. The sheer volume of votes (over 2.8 million on IMDb) solidifies its position, making it harder for a small group of critics to sway the ranking.
or your saved bookmarks to trace where you originally read it. the shawshank redemption index