SEMAINE D’ETUDE SUR LE ROLE DE L ANALYSE ECONOMETRIQUE ETC. 
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the empirical side, the assessment of quarterly data sets new 
standards of fact finding, standards that are highly influenced 
if not called forth by the subject-matter considerations embodied 
in the model building. For another thing, causal chains and 
interdependent systems have turned out to be genuine inno- 
vations in dynamic model building, not only in econometrics 
but in the wide realm of nonexperimental model construction. 
At the level of the stochastic foundations of model building the 
innovation has posed new types of problem; the debate of the 
1950’s on the rationale of simultaneous equation systems shows 
that it has taken a long time to sort out and come to grips with 
these key issues. As to the design and actual construction of 
macroeconomic models, several projects are in the picture, of 
different types, of different size, and at different stages of com- 
pletion. It is an important task to subject the accumulated 
material to systematic scrutiny and comparative studies, with a 
view to assess the theoretical and practical value of the achieve- 
ments, and, what is perhaps even more important in the present 
stage of development, to obtain guidance for further work. 
The present report focusses on three specific aspects of 
macroeconomic models: 
1) The three types of simultaneous equation systems 
known as vector regression (VR-), causal chain (CC-) and 
interdependent (ID-) systems are presented as three levels of 
generality in the mathematical design of dynamic models. The 
step from CC- to ID-systems is crucial from the point of view 
of the operative use of (a) the behavioural relations, and (5) the 
reduced form. Thus in CC-systems all relations (a)-(b) can be 
specified as eo ipso predictors, that is, as conditional expec- 
tations subject to random disturbance, whereas ID-systems 
allow such specification for relations (b) but in general not for 
relations (a). This parting of the ways is the stochastic aspect 
of the much-discussed feature that the behavioural relations 
of CC- but in general not of ID-systems are designed for a 
[2] Wold - pag. 3