SEMAINE D'ÉTUDE SUR LE ROLE DE L’ANALYSE ECONOMETRIQUE ETC. 151

procedures of hypothesis testing. In experimental situations
the empirical testing of a model can be based on replications
under controlled conditions. It is here a recognized principle
to treat the experiment as self-contained, not allowing the test
procedure to exploit any information outside the observed
sample (!?). For the testing of a variety of models a great
many routine techniques are available that are of maximum
power under the specified experimental conditions. In nonexperimental
 situations the principle of the self-contained experiment
 1s an unattainable ideal. Instead, approaches come to
the fore that in a more or less systematic manner exploit other
sources of information than the theoretical model and the empirical
 observations used for the estimation of its parameters.
Such sources include comparisons with the results of similar
or related models constructed for other regions or time periods;
testing the validity of the model by ancillary theoretical arguments
 ad hoc; and, first and last, predictive tests where forecasts
 from the model are followed up by observation ex post
and comparison with the actual course of events. Confrontation
with fresh evidence is, clearly, the real touchstone for the
scientific validity of the model as well as for its practical use.
Specific reference is made to KLEIN-BALL-HAZLEWOOD-V AN-DOME’s
 macroeconomic quarterly forecasting system for UK,
Ref. 37, and its predictive testing, Refs. 38 and 39. Here is
a keen follow-up study that without hesitation sets forth how
the predictions conform or fail to conform to the actual developments,
 and the ensuing lucid and instructive comments sort
out the weak and strong points of the model. Such follow-up
studies are highly important, and indeed an indispensable supplement
 to the published models, both for improving the model
subject to scrutiny, and as a guide for other related forecasting
projects. Some twenty models have been constructed in seven
different countries for predicting the boom-recession pulsations

(**) Stated by R.A. FIsHER (1935), the principle has been brought te
full significance by 1. TUKEY (1954)

2 Wold - pag. 27