SEMAINE D’ÉTUDF SUR LE ROLE DE I ANALYSE ECONOMETRIQUE ETC. 
NC 
As far as I have understood Professor DORFMAN, I am in broad 
agreement with him, but I think that our discussion today shows 
the need for some clarification of ideas which can only be done 
through words and therefore through the use of agreed meanings 
of words. 
AILAIS 
I must stress that there is a very good reason for my not comp 
letely agreeing with Prof. FriscH. There is a very great difference 
between three types of model: explanatory models, forecasting 
models and decisional models. This difference is the following. As 
far as the explanatory model is concerned there is a judge, you can 
verify your explanation when vou observe the facts. The same is 
true when you have a forecasting model. Your forecast may be 
wrong, but you can see if it is right or wrong. But when you 
develop a decisional model, what is the criterion of truth? I cannot 
see that there is one. You may think « I am neutral ». You may 
think this is always true, but you can be wrong; and if I think 
« you are not neutral » and if you think « I am neutral », and if we 
are in disagreement, who is to decide? You see here a very great 
difference between the first two types of model and the third. For 
the first two models there is a judge: nature. Nature can answer 
« You are right » or « You are wrong », but with a decisional model 
nobody, nothing can answer. 
MAHALANOBIS 
Neutrality is a word which we should not press too far because 
even in gathering facts it is necessary to have a conceptu-! frame- 
work; in one sense, you can collect only such facts a: vou are 
looking for. Also, all observed facts would be affecte“ *  -rrors 
of observation arising from personal bias. One has ‘, even 
farther; ultimately, according to the HEISENBERG principle .: un- 
[1] Stone - pag. 107