hiː mˌeɪd kˌɑːntɹɪbjˈuːʃənz tə θɹˈiː mˈeɪn ˈɛɹiəz ʌv ˌiːkənˈɑːmɪks: ˌiːkənˈɑːmɪk hˈɪstɚɹi, kəmpˈæɹətˌɪv ˌiːkənˈɑːmɪks ænd ˌiːkənˈɑːmɪk ɡɹˈoʊθ.
He made contributions to three main areas of economics: economic history, comparative economics and economic growth.