SEMAINE D'ÉTUDE SUR LE ROLE DE L’ ANALYSE ECONOMETRIQUE ETC. 
107 
modification of its individual elements without requiring each time 
a complete reconstruction of the entire system. 
FRISCH 
Time will not permit now to go into a detailed discussion ot 
what is an explanatory model, what is a forecasting model and what 
is a decision model, but there is one point which I must mention 
regarding a decision model, to avoid misunderstanding. When we 
start out consciously to build a decision model we begin by an attitude 
which in a sense is neutral, At this stage we are not at all deciding 
anything about what the outcome ought to be. We are to begin with 
perfectly neutral in this respect. We as scientific analysts are per- 
fectly neutral even in another respect, namely regarding what the 
preference function ought to be. This is a matter to be decided by 
the politician not by the scientific analyst. True enough the scien- 
tific expert will have to help the politician with respect to the 
form, i.e. the language in which the function is expressed, but 
certainly the scientist has not to decide the substance matter ex 
pressed by the preference function, therefore, in these very funda- 
mental aspects we are still neutral when we decide to work cons- 
ciously on the construction of decision models. There is no political 
attitude involved. 
DORFMAN 
Some time ago, in discussing this methodological problem, Pro- 
fessor LEONTIEF called to mind a very fruitful standpoint which 1 
always associate with the name of KARL PopPPER, though he probably 
did not originate it. That is: scientific advance is an iterative process. 
The models we build, the terms we use to express them, the objectives 
for which we build the models, the measurements which they dictate 
and on the basis of which we verify them — all these are in constant 
interplay and as we learn from each step we revise all the others 
1] Stone - pag. 105