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.
This is a great book. If you've ever had anything to do with the Aussie music Industry or would like an insight read this. It's funny but doesn't shy away from dealing with the serious issues too. A great book for travelling as it's hard to put down. The only problem is trying not to laugh out loud!