Beyond Six Billion Forecasting the World's Population (2000) / Chapter Skim
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Appendix E: Simluating Migration Projections
Appendix E: Simluating Migration Projections
Pages 318-325
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From page 318... ...
Since most net migration rates are close to zero, being on average proportionally smaller than crude birth or death rates, error in them may be proportionally larger. However, we are looking not at proportional error but at raw error.
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From page 319... ...
Zero projections also understate the number of net migrants, but constant projections overstate the number. Looking at absolute error permits comparisons of the
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From page 320... ...
For 5- and 10-year projections, the constant assumption gives smaller absolute errors than the zero assumption, and therefore more precise net migration rates. For all longer projections, however, the zero assumption produces less absolute error than the constant assumption.
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From page 322... ...
The zero assumption, on the other hand, produces underestimates of net migrants. Projecting migrants as zero still appears better than projecting them as constant (absolute errors are smaller)
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From page 323... ...
The results of this differentiated approach are intermediate between those of the constant projection and the zero projection, where absolute error in net migration rates is concerned (see Figure 6-4~. Where absolute error in the number of net migrants is concerned, the differentiated projection produces essentially similar results to the zero projection (Figure E-2.
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From page 324... ...
tween 1950 and 1995 makes the simulations look substantially more accurate (see Figure 6-4~. Countries that did not experience such a quake have only 60 percent of the absolute error in net migration rates of all countries, in contrast to countries that did experience such a quake, which have three times the absolute error of the average country.
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From page 325... ...
Differentiating countries, allowing constant migration for industrial countries and simply distributing the immigrants across other countries in proportion to population, appears to be an improvement over keeping migration constant everywhere. It is still slightly worse than the zero migration option, but this result nevertheless suggests that further improvement may be possible.
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