SEMAINE D'ÉTUDE SUR LE ROLE DE L ANALYSE ECONOMETRIOUE ETC. 171

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(B'

when defined as a bi-expectational system. We see that an inter
dependent system when written in the classic form (A) has the same
numerical parameters as the corresponding bi-expectational system
 (B). Hence the problem of parameter estimation is precisely
the same for the two versions of the model,
Professor FISHER’s reference to the pioneering work of J. F
MUTH, « Econometrica » 29 (April 1961), is greatly appreciated.
MuTH’s hypothesis of rational expectations opens up vistas towards
highly fruitful syntheses by assuming that expectations in the economic-psychological
 sense are in the first proxy equal to expectations
 in the sense of probability theory. In the context of my paper,
the conceptual distinction between the two notions of expectation
is referred to on page 32. To simplify matters in a first approach.
MuUTH considers market models of the cobweb type and assumes
that they are deterministic except for the supply relation, and he
makes a most interesting comparison with other theories of economic
expectation in the realm of cobweb models. The illustration in terms
of cobweb models makes a point of contact with my own studies;
see especially Ref. 30. The contact is tangential, and there is little
or no overlapping between the problems under analysis. MuTH
has explored the models with regard to economic-psychological expectation,
 and economic-psychological vs. probabilistic expectation;
my own interest has focused entirely on the rationale of probabilistic
expectation, and in particular on the general rules for operating with
probabilistic expectations.
Professor FISHER comments that the coefficient of an expectational
 variable is a meaningful parameter « only » in case there is
no difference between the economic-psychological and the probabilistic
 expectation. I have here put « only » within quotation marks
hecause I think the statement is somewhat too strong. Specifically

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Wold - pag. 57