Imdb is responsible for lowering ratings of The kashmir files. They intentionly lower the film rating because they had detected some so-called unusual activity in voting process. you can see a notification when you search for kashmir files in Imdb. Now They are using a formula by comparing the mean of only top 250 ratings. As far I know Imdb is not mentioning how do they choose those top 250 ratings. That means Imdb will not consider any new ratings after those 250 ratings.