(Econometrics is) the unification of economic theory, statistics and mathematics. - Ragnar Frisch

I have insisted that econometrics must have relevance to concrete realities, otherwise it degenerates into something which is not worthy of the name econometrics, but ought rather to be called playometrics.

There is also present another source of energy operating in a more continuous fashion and being more intimately connected with the permanent evolution in human societies.

[The] length of the cycles and the tendency towards dampening are determined by the intrinsic structure of the swinging system, while the intensity (the amplitude) of the fluctuations is determined primarily by the exterior impulse. An important consequence of this is that a more or less regular fluctuation may be be produced by a cause which operates irregularly.