358 PONTIFICIAE ACADEMIAE SCIENTIARVM SCRIPTA VARIA - 28

If ©, is put equal to 0.69, the average amortisation period
for investment, ©,, is

(334-31) © Je | #
, = © De EE
0. df

© - (1-21),

4-56 - 0.684 x 0.69
0.316

whence

O,=12.0

T'his value must be compared with the values shown in tables 8,
9 and I1 of 0.56, 8.15, and 12.18.

9) Taking hypothesis (H) in conjunction with table o,
the average amortisation period of the primary inputs corresponding
 to investment I is 8.15, whereas it is 12.9 in the
calculation immediately above. At first sight, these figures
appear to be rather low for the entire range of equipment and
structure (1).

() At all events, it should be borne in mind that, independently of the
basic assumbtions of the exbonential model, we should have (condition
(23-12)

Yc
ec
= I—vyc (i—p)
2 relation which holds for primary inputs taken as a whole whatever the
function ¢(6).
This condition depends onlv on the assumption of invariance over time

11] Allais - pag. 162