Amazon calculates a product’s star ratings based on a machine learned model instead of a raw data average. The model takes into account factors including the age of a rating, whether the ratings are from verified purchasers, and factors that establish reviewer trustworthiness.
This is been an outstanding resource! My wife is new in the business (two years now) manages about 85 units and this has answered a great many of her nagging questions. And it has been used as a reference for new ones that come up in between time. We both recommended highly!