To calculate the overall star rating and percentage breakdown by star, we don’t use a simple average. Instead, our system considers things like how recent a review is and if the reviewer bought the item on Amazon. It also analyzes reviews to verify trustworthiness.
What is there to say. Krugman and co-authors are leaders in their field. They write clearly, have material that is state-of-the-art in International Economics. Krugman's other etexts/ebooks are excellent as well.