08 
PONTIFICIAE ACADEMIAE SCIENTIARVM SCRIPTA VARIA - ; 
of this they find themselves forced to replace the essentially symbolic 
concept of traditional economic theory by concrete operational con- 
cepts referring to directly observable and measurable facts with which 
a business man, an engineer or a practical economic planner has to 
reckon in the couse of his every day activities. 
In some instances we find ourselves seeking collaboration with 
other disciplines. In describing and analysing processes of pro- 
duction, an economic model builder must be prepared to speak the 
language of a production manager and of an engineer; in dealing 
with the structure and behavior of households, he must be prepared 
to speak the language and use the concepts of a demographer and 
a social-psychologist. 
The time when the economist or the econometrician could limit his 
efforts to construction of mathematical models — or devising more 
sophisticated methods of statistical inference — is passing fast. He 
has to take increasingly active part, not only in the actual use of these 
models and application of these methods, but in the organization and 
the direction of the fact gathering activities without which all theory 
and methodology will continue to be no more than intellectual 
exercise. 
VIAHALANOBIS 
There is one point in Professor WoLD’s observation about which 
[ am not clear. When he said « forecasting » did he include 
i targets »? It is possible to take suitable action to attain certain 
targets which are considered desirable; this is the system, for exam- 
ple, in central planning in U.S.S.R. It is not forecasting based essen- 
tially on historical experience or time-series analysis but setting up 
certain targets which it is desired to achieve over a certain period of 
time. Would Professor WoLp include setting up of such targets 
within forecasting? 
1] Stone - pag. 96