Comparative advantage is a theory evidenced by using economic models. I should stop there; anyone who has taken more than one class in Economics will tell you that an "economic model" relies on the idea of ceteris paribus : "all other things equal." In theory, this is the only way we can interpret the world around us. If we hold other things constant, then the relationship between X and Y will become more clear. Economics as a discipline is more concerned today with the field of econometrics. The basis of econometrics itself rejects ceteris paribus , because regression analysis is only as accurate as the multiple variables being accounted for. Things are not being held constant in regression analysis. It is the duty of an econometric analyst to be fair, detail-oriented, and comprehensive. In excluding variables, he or she erodes the integrity of the regression analysis. In contrast, economics is concerned with rejecting all such variables. Now, it is not suffic...