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 Usually wear a medium size shirt. Ordered the large as my previous sweater was a bit smaller than a usual medium. Loved it that much I decided to buy the large size. Very happy I did. Perfect fit, nice and warm without having to wear a jacket as well.