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.
Awesome product. When it's hard to find time to study the book, these CDs were a life saver. Listen in the car to and from work and on lunch break = 1.5 hours each day, 5 days a week. Very easy way to study for the civics test and become a US citizen.