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370 Jean Bourgeois-Pichat
adults, the aged, workers, pregnant women, newly-weds, sick persons, aliens,
household, family, village, etc. Hence collaboration is obviously necessary
between the various experts and demographers, for these latter alone are able
to give the number of units of each category, thus making it possible to pass
from average individual needs to global needs, that is, to the global production
necessary in order to satisfy those needs.
Population censuses provide the answers in all ordinary cases, but therealways
remain classes of consumers that have escaped the census and whose numbers
have to be calculated. The demographer is relied on to supply such estimates.
Demographic prospects
55. Comparing needs with possibilities, the planner generally finds that the
former are greater than the latter and he draws up a plan of investment designed
to reduce the difference, hoping to eliminate it altogether in due course. However
as a rule, this final goal is found to be out of reach within a strictly limited time,
and plans are spread over a period of years. All investment implies saving of
some kind,16 that is to say, a restraint on consumption, and if this restraint is
too severe, the population feels itself to be under compulsion. Where there
is a difference between needs and possibilities, the shorter the duration of the
plan the greater the compulsion necessary. Consequently, this duration will be
in terms of the capacity of the population to suffer, and the planner will, as a
rule, prepare several plans of varying duration, leaving it to the political authori-
ties to decide which one will not go beyond the point acceptable to the popula-
tion.
In the case of each of these plans, it is indispensable to know what the needs
will be throughout its entire duration, and it is here that the demographer again
has his part to play, for he must be able to calculate not only the existing num-
bers of the various classes of consumers, but also those for the years iminediately
ahead.
Prospective calculations have led to the invention of special methods which
now form an important side of demography: the calculation of demographic
prospects, or again, of population projections. For a long time we were satisfied
with very simple calculations, such as population prospects according to age
and sex. Lately we have undertaken the calculation of prospects more useful to
the planner, dealing with households, families, school population, urban
population, etc. However, this is only a beginning and the field of activity is
vast. With electronic computers it is now possible to deal with sectors which,
without them, we have so far been prevented from going into. They also enable
us to vary our assumptions.
Working population prospects
56. Assuming that the means of production are there, they then have to be used,
and for that we need labour. The investment plan will have to be set out in
terms of manpower and not confined to planning the building of factories and
manufacture of machines. It will also have to show the number and the structure
of the working population required to turn the means of production to ac-