"Along with Frisch and others Tinbergen developed the field of econometrics, the use of statistical tools to test economic hypotheses. Tinbergen was one of the first economists to create multiequation models of economies. He produced a twenty-seven-equation econometric model of the Dutch economy, and his 1939 book, Business Cycles in the United States, 1919–1932, includes a forty-eight-equation model of the American economy that explains investment activity and models American business cycles."