SEMAINE D'ÉTUDE SUR LE ROLE DE L’ANALYSE ECONOMETRIOUE ETC. 
631 
empirical law, stating that the proportion of income spent on 
any type of goods changes as per-capita incomes increase has 
been confirmed ever since, and evinced by all the econometri- 
cians who have been concerned with empirical work on de- 
mand (°). 
These results are in fact no surprise. It should not take 
long to realise that what they reveal is a basic tendency inhe- 
rent in the human nature of the consumers. We shall go into 
this matter in the next section. Meanwhile we may safely 
draw the conclusion that all the models of economic growth so 
far developed have adopted a set of hypotheses which are 
‘ncompatible with one of the most fundamental empirical laws 
of economics. Since increases in per-capita income necessarily 
imply non-proportional expansion of demand, and since techn- 
ical progress means increases in per-capita incomes, then the 
introduction of technical progress in any dynamic model ne- 
cessarily implies a non-proportional expansion of demand. The 
assumptions adopted in all macro-economic models of growth 
are therefore unaccentable. 
6. The evolution of demand in time 
The practical importance of ENGEL’s law has always been 
recognized by all those who, on any occasion, have been en- 
gaged in empirical work on demand. Yet, in spite of the fact 
that it was discovered more than a century ago, very little work 
has been done to try to take advantage of the information it 
gives and to incorporate it into the theory of consumer’s beha- 
viour. (Bits of piece-meal theory can be found only in the 
works of the econometricians who — faced with facts — have 
alwavs been compelled to make additions and to adapt an in- 
(°) See, for example: R.G.D. ALLEN and A.L. Bowrey, Family Expen- 
diture, London, 1935; and also: H.S. HOUTHAKKER, An International Com- 
parison of Household Expenditure Patterns, Commemorating the Centenary 
of Engel’s Law. in « Econometrica ». 1957. 
10} Pasinetti - pag. OI