SEMAINE D'ETUDE SUR LE ROLE DE L ANALYSE ECONOMETRIOUE ETC. 
range economic models; the differences would be too deepgoing. I. 
would be more instructive to have one clearcut model of each type, 
and compare the models to explore where and what the relevant 
differences are. 
My own report to the Study Week, when it comes up, will deal 
with three specific aspects of model building. I had prepared some 
notes about the general principles of model building as an introduc- 
tion to the oral presentation of my report. Then when I heard 
Prof. MAHALANOBIS’ plea for a general consensus about basic termi- 
nology and notions, I felt it was in line with his plea to cut out these 
notes and present them right now, as a contribution towards unifying 
our basic notions about model building 
LEONTIEF 
I would like to comment on the relationship between theoretical 
construction and factual observation within the framework of Pro 
fessor STONE’s presentation. The relationship is essentially an ite 
rative one, 
The theoretical model in its first experimental version is formulated 
so as to be capable of being implemented with the available, or at 
least, obtainable factual information. At the same time it should 
serve as a guide in determining the most promising direction of 
further empirical inquiry. 
The bulk of official statistics is still being gathered to serve va- 
rious administrative needs or to supply up-to-date information tc 
general users. However, an ever larger volume of data is being col- 
lected with the specific purpose of being fitted into explicitly formu. 
lated analytical models. 
In the past the theorist was too often inclined to leave the respon 
sibility for the factual implimentation of his conceptual schemes to 
the statistician. Now the model builders have come to realize that 
they have to take active part in the preparation and planning — if 
not the actual performance — of the data gathering task. As a result 
‘1] Stone - pag. 95