SEMAINE D’ÉTUDE SUR LE ROLE DE L’ANALYSE ECONOMETRIOUE ETc. 145

where A. B and z, are the same as in (18), while (152)

58)

y" =E(v,IR z)=R

is the vector of conditional expectations of the current endogenous
 variables as given by the reduced form, which as before
ts assumed to be given by (21)-(22) with (23), to repeat

(50)

B -

Then the following relation can be established,

(60)

E(y ly, z)=A vy. +B ¢

showing in conjunction with (58) that the BEID-system is biexpectational
 in the sense of 1.2 (3).
As to the proof of (60), we note that the model becomes
deterministic if we respecify the primary form (57) and the
reduced form (59) by deleting all residuals and in the left-hand
members substitute y; and y, for y, and y,. This follows as
an immediate corollary from the substitution theorem (53)-(54),
allowing z to be a vector variable.
In the debate on « simultaneous equation systems » it has
been a key point what causal interpretation, if any, can be
given to the parameters a; of the behavioural equations in the
primary form (18) of ID-systems (again, see footnote 6). The
parameters a;, being numerically the same as in the corresponding
 BEID-system, relations (57) and (60) give the answer that
the parameters allow the same cause-effect interpretation as
in CC-systems. except that whenever a current endogenous

(59) In the manuscript as presented at the Study Week, the matrix R
was missing in E(y, | R z,) in formulas (23) and (58). Cf. the paper (b)
referred to in the subseauent discussion. page 6. footnote (1

2] Wold - pag. 31