72 PONTIFICIAE ACADEMIAE SCIENTIARVM SCRIPTA VARIA - 28 
with 
0 
E(y,lz, 
RP - 
We note the following general features of vector regression 
systems: 
1) The system contains one (and only one) explanatory relation 
for each of the current endogenous variables; 
2) In each relation, all of the explanatory variables are pre- 
determined; 
3) Each relation is an eo ipso predictor subject to random 
disturbance. 
[.2. Causal chain (CC-) systems. 
The general formula for causal chain (also known as recur- 
sive) systems is in the linear case given by 
(10) 
Vir=Li(y14 Vars +, Vici Nieto Vio» ++"5 Xp Xi_ 1» …)+U;, 
where ¢=1, ..., n; the functions L; are linear; and L; is as- 
sumed to be an eo ipso predictor of y., for all 7 and ¢, 
(IT) Elyse Yatr wor Victts Verts Vr-ns +05 Xp Xp_45 ++) 
Lyi Var oes Vi-1,e5 Veste Ve-2 +03 Xt oon) 
To give the system (10)-(11) in matrix form we write 
à" +B 3 
12) 
with 
E(yly", 2)=A y, -B Z, 
2] Wold - pag. 8