We may perhaps start by throwing all kinds of production into one variable, all consumption into another, and so on, imagining that the notions 'prod… - Ragnar Frisch

In the last decade's intensive study of all sorts of social and economic time series, it has become clear, it seems to me, that the usual time series technique is not quite adequate for the purpose which the social investigator is pursuing... We want to find out on more or less empirical grounds what is actually present in the series at hand, that is to say, what sort of components the series contains.

To proceed from assumptions about an abstract theoretical set-up and from them to draw conclusions about the observable world and to test - by rough or more refined means - whether the conformity with observations is "good" enough, is indeed the time honoured procedure that all empirical sciences, including the natural sciences, have used. I shall therefore not plead guilty of heresy even if I do work with choice-theory concepts that are not invariant under a general monotonic transformation of the utility indicator.

In reality the cycles we have the occasion to observe are generally not damped. How can the maintenance of the swings be explained? Have theses dynamic laws deduced from theory and showing damped oscillations no value in explaining the real phenomena, or in what respect do the dynamic laws need to be completed in order to explain the real happenings? They (dynamic laws) only form one element of the explanation: they solve the propagation problem. But the impulse problem remains.