326 PONTIFICIAE ACADEMIAE SCIENTIARVM SCRIPTA VARIA - 28 
derived from the exponential model appears to concord very 
well with the results obtained from analysis of available data 
on durable goods in all cases where a sufficiently large compe- 
titive market in these goods exists (1) (2). 
An attempt to derive the fonction ¢(6) directly, at least 
approximatively, can be made with the help of statistics of the 
distribution of the working population. This analysis involves 
major difficulties, but at first sight seems to produce results in 
conformity with an exponential form of ¢(8) (3). 
The length of the production period 6=y is of the order 
of 3.5 years for the U.S.A. For the average amortisation period 
® =vc, from (251-6) 
(326-2) 
& 
B 
— 60 
Whence, for Ô=3.5 and p=1.7% (*), © is derived for 
the U.S.A. as 3.72, i.e. a value which differs little from that 
5 
of 
(1) Arras (1960 A), p. 22-23. 
2) It may be objected that in a rigorous formulation, the composition 
ot different exponential amortization functions cannot result in an expo- 
aential global amortization function over the whole range of variation (0, oo) 
of @. Nevertheless, over the useful variation interval (o, 100) of 0, use 
of this type of function is certainly possible. as it involves a rather low 
-elative error. 
() Arrais (1960 A), § 45. 
(*) Equal, as a first approximation. to the rate of population growth in 
the T7.S A 
11] Allais - pag. 130