Amazon calculates a product’s star ratings using a machine learned model instead of a raw data average. The machine learned model takes into account factors including: the age of a review, helpfulness votes by customers and whether the reviews are from verified purchases.
I'm a person who only really sings in my car, where no one else can hear me... I got the Singers Companion to learn more about singing as an art and it's amazing what people like Vince Jones, Sharny Russell and many more share in the book about techniques, their backgrounds and their passion for the joy of song! A lovely read!