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 pa- 
rameter in both cases. Then the link, the essential element of in- 
variance, 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 misunderstand- 
ing about the mathematical aspects. Yet there are at least three pos- 
sible 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