I believe that economic theory has arrived at a point in its development where the appeal to quantitative empirical data has become more necessary than ever. At the same time its analyses have reached a degree of complexity that require the application of a more refined scientific method than that employed by the classical economists.

Ragnar Frisch (1926); Quoted in: "Ragnar Frisch 1895-1995." O. Bjerkholt, 1994.