But in the second phase , all of these theories can still be categorized into 4 kinds : dynamic comparative advantage theories , such as the new factors theories by baldwin and kenen , the life - cycle theory by vernon and hirsh , etc ; intra - industry trade theories such as product differentiation model by stiglitz and dixit , the strategy trade theory by spense , brander and krugman , and so on ; the endogenous trade theory such as technology overflow effect and learning curves theory by romer and krugman , the neo - classic trade theory by tucher and young , and the like ; and the competitive advantage theory by michael porter 在這一時期,經(jīng)濟學家們提出了形形色色的理論,出現(xiàn)了“百家爭鳴”局面?;旧峡梢詺w于以下四大類型:一是動態(tài)的比較優(yōu)勢理論;二是產(chǎn)業(yè)內(nèi)貿(mào)易理論;三是內(nèi)生國際貿(mào)易理論;四是競爭優(yōu)勢理論。各個階段的比較優(yōu)勢理論有其時代特點,但一個共同點是:比較優(yōu)勢始于成本差異,并一直沒有突破成本差異,而不考慮產(chǎn)品的附加值。