SEMAINE D'ÉTUDE SUR LE ROLE DE L’ANALYSE ECONOMETRIQUE ETC. 415 
of the process generating the disturbances in terms of such 
omitted variables and such serial correlation. 
We shall assume that the disturbances to any equation are 
made up of three sets of effects. The first of these will consist 
of the effects of elements common to more than one sector — in 
general, common to all sectors. The second will consist of the 
effects of elements common to more than one equation in the 
sector in which the given equation occurs. The third will consist 
of effects specific to the given equation. 
Thus, let the number of equations in the Ith sector be n, 
We write: 
(5.4) 
where 
(5.5) 
is a vector of implicit disturbances whose effects are common 
(in principle) to all equations in the model and ¢' is an #; x K 
constant matrix: 
(5.6) 
is a vector of implicit disturbances whose effects are common 
(in principle) to all equations in the Ith sector but not to equa- 
tions in other sectors; W' is an » - H, constant matrix: and 
(5.7) 
31 
Fisher - pag. 31