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PONTIFICIAE ACADEMIAE SCIENTIARVM SCRIPTA VARIA - 28 
daily practice, direct observation becomes possible and indirect in- 
ference dispensable, The empirical implementation of an analytical 
model comprising large sets of simultaneous, or at least interrelated 
equations, does not require any more indirect estimation of large sets 
of parameters imbedded in corresponding large sets of simultaneous 
statistical equations. The observations can be made one by one and 
essentially independently of each other. If and when this happens 
controversies concerning the choice among alternative methods of 
statistical estimation might lose the dominant position which they 
now occupy in discussion of econometric problems. 
FISHER 
Professor LEONTIEF in his interesting remarks looks forward to 
the day in which the use of highly disaggregate data will enable 
us to concentrate less on simultaneous equation problems. While 
I think that such a day is probably very far off, I do agree that 
such problems become of less importance as one goes to more and 
more disaggregated data. On the other hand, there are at least 
some forms of disaggregation which do not lead to this desirable 
result. For example, as I argue in my paper, disaggregation in 
the form of securing data for smaller and smaller time periods does 
not avoid the simultaneity problem since the disturbances for such 
time periods are likely to be serially correlated. Whether other forms 
of disaggregation aid in avoiding simultaneity seems to me likely 
to depend on the model and the type of disaggregation. I think 
that so long as one is interested in models of the entire economy, 
simultaneity will remain an interesting question, even if one deals 
with data in terms of individual units. This is so, because it remains 
true, for example, that the income identity holds summing over all 
units. 
While simultaneity introduces numerous problems, I think one 
should beware of the attitude (which I am aware is not Professor 
LEONTIEF’s) that simultaneity problems should be avoided at the 
61 Fisher - pag. 78