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 reason- 
ably acceptable at least as a first approximation. The hypo- 
thesis (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