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 nonexpe- 
rimental situations the principle of the self-contained experi- 
ment 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 em- 
pirical 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 argu- 
ments ad hoc; and, first and last, predictive tests where fore- 
casts 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 deve- 
lopments, 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 sup- 
plement 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