how do you calculate comparative advantage 
comparative advantage is usually measured in opportunity costs or the value of the alternative goods that could be produced with the same resources this is then compared with the opportunity costs of another economic actor to produce the same goods for example if factory a can make 100 pairs of shoes with the same resources it takes to make 500 belts then each pair of shoes has an opportunity cost of five belts if competitor factory b can make three belts with the resources it takes to make one pair of shoes then factory a has a comparative advantage in making belts and factory b has a comparative advantage in making shoes 