SEMAINE D’ETUDE SUR LE ROLE DE L’ANALYSE ECONOMETRIQUE ETC. 
455 
Looking upon the matter from the view-point of an economist 
giving advice to a politician, I would suggest that, when we speak 
of an estimator and the properties of estimators — we accept to put 
as the main classification: 1) Purposefully useful; 2) Purposefully 
irrelevant and 3) Purposefully detrimental. 
I will explain what I mean by « purposefully useful ». Every 
estimator must be thought of in terms of the purposes for which 
we are going to use to coefficient or magnitude estimated. In this 
particular case the purpose is perhaps a political one. You must say 
that this is vague. Yes, I am sorry to say that these words are 
vague and they cannot be defined precisely because the purpose 
will vary from one application to another, so therefore the specifi 
cation of what is meant by these properties must vary and can only 
be made more precise if you are explaining very explicitly for what 
purpose you are going to use your analytical results. Many of these 
properties of estimators which are fundamental from the view-point 
of application are very difficult to handle. Of course we like dif 
ficult problems, provided they are not beyond the limit of our 
ability. Then it would be very interesting to handle the problems. 
But when they pass beyond this stage it is very tempting to pick 
out certain properties which are not in true sense purposefully useful 
— they may even be purposefully detrimental but they have the 
property that I am able to handle them. 1 may decide then to 
work with these concepts instead of the really important ones which 
I am not able to handle. Let me take an example. I am going 
to multiply 13 by 27. I scratch my head and I think. « Oh, multi- 
plication is such a terribly difficult operation, but I am very good 
at adding fiures, so why don’t I add instead the two numbers 13 
and 27». You wouldn't think that that was a very useful pro- 
redure. 
I will illustrate what I have said by taking the two words 
« unbiased » and « consistent », I am afraid that we have, to some 
extent, been carried away by the common meaning of these words. 
What is « biased » and « unbiased n? I would rather have pre. 
ferred to use the term « not immoral » instead of « unbiased », be: 
6] Fisher - pag. 71