360 PONTIFICIAE ACADEMIAE SCIENTIARVM SCRIPTA VARIA - “ 
However, to obtain the average amortisation period for 
the corresponding primary inputs, this figure must be increased 
by the average length of the production period for investment 
goods, whose order of magnitude is 8'=3.59 (!). The average 
duration of the amortisation period for the primary inputs cor- 
responding to investment is then 
®,=10.2+3.59=13.79 
which may be compared with the estimates of 8.1 5 in Table g 
and 12.9 in § 334-8. From this point of view, the approxim- 
ative hypothesis (H”), which leads to a value of 12.0 (?) is 
to be preferred to the interpretation underlying hypothesis (H), 
which leads to a value of 8.15. 
Clearly, if it is assumed that the general formulation of 
che exponential model is valid, the difference between the 
theoretical value of 12.9 calculated under hypothesis (H”) and 
the observed value of 13.8 may be explained by the inaccuracy 
of the assumption in (H”). But in the light of the appealing 
nature of this assumption, at least as a first approximation, 
the concordance of the orders of magnitude of the two estim- 
ates can be considered as underscoring the validity of the 
exponential model. At the same time, the results derived using 
interpretation (H) show that this hypothesis offers only a 
roughest resemblance to realitv. 
10) Since the average production period for consumed 
income is ©, it may be assumed as a first approximation that 
‘he average production period for investment goods is also 6. 
It is then also possible to represent as a first approximation 
the reality by the following model (Hypothesis H”). In each 
(") § 334-5. 
(3) § 334-8 
11] Allais - pag. 164