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Multilingual Demographic Dictionary, second unified edition, English volume

Residual method

Multilingual Demographic Dictionary, second unified edition, English vol.
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Residual method  (RESIDUAL method)

Where it is not possible to determine migration directly, indirect estimates of net migration may be obtained by the residual method 1 or method of residues 1 in which the change in population between two dates is compared with the change due to natural growth; the difference between the two figures is attributed to migration. The vital statistics method 2 consists of computing the difference between total population change, as assessed from two censuses, and natural increase (701-7) during the intercensal period. The survival ratio method 3 is commonly used to estimate net migration by age; it does not require actual death statistics. Survival ratios are derived from life tables and are applied to a sub-population in one census to give expected numbers by age at the time of the other census. A comparison between the observed and the expected population may be used to estimate the balance of migration by age for the subpopulation. When place-of-birth statistics 4★ (813-3) by age and current residence are available in two consecutive censuses, it is possible to make indirect estimates of migration streams.

  • 2. The equation showing that the difference between total population change and natural increase is equal to migration has sometimes received the name of balancing equation. In order to use it for the estimation of net migration, one must assume that omissions (230-3) and multiple countings (230-5) are equal for both censuses.
  • 3. The major variants of this procedure are called the life table survival ratio method and the national census survival ratio method. In the forward survival ratio method, the population at the beginning of an intercensal period serves to estimate the expected population at the end of the period, and the procedure is reversed in the reverse survival ratio method; the average survival ratio method combines these two approaches.