748

PONTIFICIAE ACADEMIAE SCIENTIARVM SCRIPTA VARIA - 28

eo

— A QUASI-STATIONARY PROCESS WITH
VARIABLE GROWTH RATE

Definition

120. I will use the expression « a quasi-stationary process
with variable growth » to denote a process characterised by

a) invariance of the difference i(¢) - P(#) over time;
b) invariance of the characteristic function © over time
for a given value of i -p (1).

We then have

(120-1)

(120-2)

(8) - p(é)=i

p(¢, 0) =1¢(0)

where #’ is a constant.
The assumption underlying (120-1) appears to be reasonably
 acceptable at least as a first approximation. The hypothesis
 (120-2) is equivalent to assuming that the composition
of the labor force is constant over time. This, too, is a quite
natural assumption, at least as a first approximation.
These two relations enable the general relationships which
have already been derived to be considerably simplified.

(') The alternative hypothesis in which ot 0) is assumed invariant over
:ime could also nsefullv be studied

11] Allais - pag. 52