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.
While clearly written for British expectant mothers because of the information about the NHS system, I found it really informative and helpful. Even as a second time mom, I learned more about pregnancy and childbirth. While I'm not sure I'd recommend the book to an American mom, I would recommend it overall.