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404 Jean Bourgeois-Pichat
Use of defective data
We now come to a series of studies of an entirely different kind.
160. The importance of demographic factors in the economic and social
advancement of the developing countries has led demographers in those coun-
tries and demographers working in the international organizations to consider
the use made of the mass of demographic statistics collected over the years in
those parts of the world. For a long time it was thought that these data were of
too poor a quality to yield any significant information on the demographic
situation in those regions.
161. The advances made in demographic analysis have led to a revision of this
attitude and, gradually, a new system of methods has been devised enabling the
best possible use to be made of defective data. In this respect, the Population
Division of the United Nations has acted as a powerful catalysing agent for the
researches undertaken. Two books have lately been published summing up the
results so far achieved. The development of these researches was due to cir-
cumstances and it is unlikely that they will be extended much in the future. The
efforts made to improve the quality of demographic statistics are beginning to
bear fruit and there are grounds for hoping that sound data will soon be
available.
I 62. One of the fundamental aims of this work on the analysis of defective data
was to establish ‘sample situations’ and to compare with these situations the
countries under investigation. In this way, some series of sample mortality-rate
tables have been drawn up representing the different stages through which
mankind passed when its mortality rate fell. Here, the Population Division of
the United Nations blazed the trail by publishing a series of such tables in a
single dimension. Further series in several dimensions followed (France, USA).
Similar researches have been undertaken in the matter of fertility, but they are
less advanced.
163. Theoretical considerations have also played their part. The concept of
stable population evolved before the last war by Alfred J. Lotka has been
debated afresh and two new concepts have emerged - those of ‘quasi-stable’ and
‘nearly stable’ populations. The former are empirical populations, that is, populations
arrived at by maintaining the fertility rate constant and varying the
mortality rate over the area defined by the sample tables just referred to. It has
been observed that these populations differ little from the stable populations.
I 64. Nearly stable populations are populations that are invariable in their
composition by age. It has been shown that, at any given moment, the relations
existing between the various characteristics of these populations are the same as
those existing in the case of stable populations.
165. The populations of the developing countries fulfil approximately one or
other of the conditions which served for the elaboration of the two concepts of