SEMAINE D ETUDE SUR LE ROLE DE L’ANALYSE ECONOMETRIQUE ETC.
SI
great generality is usually sought and frequently achieved. In
practice it is often necessary to adopt a formulation at the
same time less general than theorists would like within the
range of phenomena they consider, and less restricted in its
range. For example, the consumption functions we are using
cannot handle complementary or inferior groups of commodities
but they can handle systematic changes in preferences and also
adaptive behaviour.
Fifth, is assembling observations on which to base our
projections, we can achieve a great deal by the careful proces-
sing of existing data, but however thoroughly we do this our
knowledge remains incomplete. We must therefore try to gain
the cooperation of outside experts in practical walks of life,
who may be less well placed than we are to attempt a synoptic
view of the whole economic system, but whose specific know-
ledge is always greater than ours. The realism of our projections
can only increase as we succeed in getting more reliable in-
formation into the model.
Sixth, to be a useful tool for policy-making a model must
enable us to make not just one but many alternative projections
based on different assumptions. When it has reached this stage
the model becomes in its turn a source of information in the
light of which a policy can be drawn up. If this policy is
carried out, the model can then be used to make predictions.
Seventh, no policy can be carried out without a control
system which keeps the plan in touch with events. This con-
trol system consists of a mixture of centralised and decentralised
administrative machinery, including all private arrangements
for the management of businesses, cooperatives, labour unions
and so on. The model can be used to review the control system
and show how administrative methods might be modified so as
to improve the economy’s inherent tendency to stability. I have
not tried to formulate this range of problems because as yet we
have done very little work on them.
Eighth, it is impossible to plan unless one knows what one
‘11 Stone - pag. 81
