SEMAINE D'ÉTUDE SUR LE ROLE DE L’ANALYSE ECONOMETRIQUE ETC. 181

parameter. Let P*(x, y, GB) be the corresponding probability law
for the future, under a new economic regime, B being the same parameter
 in both cases. Then the link, the essential element of invariance,
 as between the past and the future may be the value of
3 rather than e.g. the expected value of y for given x, the latter
relation depending on the form of the probability laws P and P*

KOOPMANS

In the discussions comparing inter-dependent systems and other
systems, one element has been important which I have not heard
Professor WoLD mention in this summary. This is the idea of the
autonomy of individual equations of the interdependent systems.
My question is whether the concern with autonomy can be
conserved when we go from the ID to the BEID and alternatively
when we go from the ID to the CC svstem.

WoLDp

Since Professor KooPMAN’s question is closely related to Profes.
sor HAAVELMO’s comment, I shall reply to them jointly.
Professor HAAVELMO’s clarifying example has the advantage that
it is so simple that there could not possibly arise any misunderstanding
 about the mathematical aspects. Yet there are at least three possible
 interpretations of the example to consider.

I) Parameter §3 is symmetric with respect to the variables x, y;
for example, B is the correlation coefficient of x and y. This is the
case I thought of in the first place when finishing my previous reply
to Professor HAAVELMO by a critical remark. Parameters that are
symmetric in this sense make a conceptual category that is far
too narrow to represent all meaningful parameters. For example, a
demand elasticity with respect to price, or an interest rate, do not
possess this kind of symmetry

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Wold - pag. 67