Fisher made important contributions to utility theory and general equilibrium.[5][6] He was also a pioneer in the rigorous study of intertemporal choice in markets, which led him to develop a theory of capital and interest rates.[3] His research on the quantity theory of money inaugurated the school of macroeconomic thought known as "monetarism."[7] Fisher was also a pioneer of econometrics, including the development of index numbers. Some concepts named after him include the Fisher equation, the Fisher hypothesis, the international Fisher effect, and the Fisher separation theorem.