324 PONTIFICIAE ACADEMIAE SCIENTIARVM SCRIPTA VARIA - 28 
The exponential model thus leads to the expectation that 
the value of the capital-output ratio will differ little across coun- 
tries at different times. 
If we use COLIN CLARK’s figures, consisting of 58 estimates 
for 21 countries for different dates between 1805 and 1953, 
we find that they are lognormally distributed with a median 
value of 3.54 (1). 
The overall results are therefore as follows: 
U.S.A., 1880-1956 (median of 12 observations) . . 3.46 
U.S.A., France, U.K., 1913 (average) . . . . 3.72 
World - 1805-1953 (median of 58 observations) . . 3.54 
The concordance of these different estimates is absolutely 
remarkable. It suggests a temporal and spatial regularity 
which in any case must be explained. 
The explanation given by the model is a simple one. 
c) Constancy of the Ratio C/R, 
325. The exponential model contains a very remarkable re- 
lationship: 
325-1) 
C()=©, Rolf) 
2 
|" } 
According to this expression, statistical analysis should show 
an approximative stability over space and in time of the ratio 
of capital to primarv income. 
() Arrars (1960 A), pp. 54-57; (1062 A), p. 72: 
(?) Relation (251-9). PP. 54-57; (1962 A), p. 743 
11] Allais - pag. 128