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Demography 405
population, ‘quasi-stable’ and ‘nearly stable’. It wil readily be realized how these
concepts can be used for the analysis of the demographic data assembled in
those countries.
Electronic computers
166. We must also mention another type of research, the originality of which
resides in the use of new media of investigation - electronic computers.
As in the case of research in historical demography, this type relates to all
the sectors of demography and the only reason for placing it in a special cate-
gory is the novelty of the methods employed.
167. Electronic computers have made possible what are now known as ‘simu-
lations’. The word is a new one, but the idea is extremely old, and the demog-
raphers who formerly worked out projections using the classical methods of
calculation were really doing nothing other than simulation. They observed
what would happen to a population subjected to a given set of demographic
conditions. Because of the inadequate means of calculation then available, the
data had perforce to be simplified. The use of electronic computers now permits
of all possible complications.
The advances made in demographic analysis and the establishment of
‘sample situations’ have therefore made it possible to construct ‘models’
bearing an even stronger resemblance to actual situations.
168. But that is not all. Thanks to computers, we have been able to pass from
determinist models to probabilist models. What is happening in a population
where decisions are taken at the individual level is actually simulated. It is
sufficient to introduce laws of probability into the computer; the machine then
produces haphazardly the:demographic events corresponding to those probabil-
ities. This enables us to observe not only the trend of average values (which the
determinist models already made possible) but also their variation.
169. By modifying the laws of probability, different simulations are obtained
and in this way the demographer brings into being the conditions of a pseudo-
experiment. In real life, the behaviour of individuals is modified by population
trends and, as little is known about these modifications, simulation by elec-
tronic computer cannot be regarded as a true experiment. However, here again
progress is possible and, indeed, probable.
170. It is also thanks to electronic computers that research based on a ‘compari-
son of documents’ has recently been able to emerge from the handicraft state in
which it was hitherto confined through lack of facilities. The principle of this
research resides in the comparison of documents drawn up on different occa-
sions. We have already mentioned in connexion with mortality rates a research
project in France and another in the USA where this method is being used. In the
case of both projects, death certificates are compared with census returns. Some
Canadian demographers have set out to compare in the same way successive