[The] length of the cycles and the tendency towards dampening are determined by the intrinsic structure of the swinging system, while the intensity (… - Ragnar Frisch

When we approach the study of business cycle with the intention of carrying through an analysis that is truly dynamic and determinate in the above sense, we are naturally led to distinguish between two types of analyses: the micro-dynamic and the macro-dynamic types. The micro-dynamic analysis is an analysis by which we try to explain in some detail the behaviour of a certain section of the huge economic mechanism, taking for granted that certain general parameters are given. Obviously it may well be that we obtain more or less cyclical fluctuations in such sub-systems, even though the general parameters are given. The essence of this type of analysis is to show the details of the evolution of a given specific market, the behaviour of a given type of consumers, and so on.

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.

The propagation problem is the problem of explaining by the structural properties of the swinging system what the character of the swings would be in case the system was started in some initial situation