Free--short--Principles text by Mathew Kahn, who has left UCLA for the University of Spoiled Children, that has an unusual approach:
. . . I still see an open niche here for a challenging e-book. Unlike other Principles books, this book will be “data driven”. I will present you with an empirical economics puzzle such as “why do men earn 22% more per hour than women”? I will then walk the reader through possible economic explanations for the fact but then we will go a step further. Often there will be several possible explanations for a given set of facts. I will challenge you to work with me to devise a new experiment for figuring out which explanation is right. In this sense, we will start with a set of facts.We will use economic logic to sketch out the set of possible explanations. We will then, because we are scientists, devise a new experiment for settling which of the explanations is right. The new experiment will generate new facts and the “correct theory” should both be able to explain the first fact and the new fact while the incorrect theories can explain the first fact but not the later facts.