{10 PONTIFICIAE ACADEMIAE SCIENTIARVM SCRIPTA VARIA - 28
certainty it is not even possible to make an observation without
disturbing the system itself. We should not press the question of
neutrality in an extreme way, but take a broad view that for certain
purposes certain models would be more appropriate than others.
The point stressed by Professor LEONTIEF is extremely important
the validity and also the precision and the effectiveness of a
model to serve certain purposes which may be purely explanatory
or may be decision making or may be forecasting or may be of other
types. I think this raises questions of substance which we should
discuss; and we should, among ourselves at least, provisionally agree
on what kind of words we should use.
WoLD
I am not sure whether there is really any disagreement between
Prof. Arrars and Prof. FriscH, but their debate does confirm Prof.
MAHALANOBIS” view that it is a good thing to clarify our terminology
— not necessarily to establish it for the indefinite future, but at least
for the purpose of our discussion during the Study Week. The
question has been posed: What is a decision model, and how does
it differ from a forecasting model? It is my undestanding that
decision model and policy model are essentially the same notion. If
so, the question can be answered along the lines of a famous argument
by the distinguished Swedish economist GUNNAR MyrpAL. Political
actions, including actions of economic policy, are based on value
judgements, and it is typical that the judgements are radically
different for members of different political parties. The analysis of
economic policy and other decision systems takes the form of a
policy model, where the value judgements underlying alternative
political actions are included as specified hypotheses, hypotheses
which in themselves are politically neutral. In this way the policy
model becomes, in principle, an instrument for strictly scientific
analysis of alternative lines of political action.
‘1] Stone - pag. 108
