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5.3  Migration

In principle, it would be preferable to make separate in-migration and out-migration projections, rather than a single net-migration variable. There would, however, be little material gain in exchange for the added complexity, as migration has far less influence on age-structure, and hence support ratios, than either fertility or mortality. (The reason is that migration occurs at a wide range of ages, whereas everyone is born at exactly age 0, and most people die at ages 60 and over).

This paper is somewhat unusual in that the migration projections have been carried out in terms of rates rather than numbers. For short-term projections, the choice of numbers or rates in fact makes little difference. For long term projections, it can be argued that the use of rates is more sensible. This is most obvious for out-migration, which is clearly related to the size of the population. However, for New Zealand, it is likely to be true for in-migration as well. A significant proportion of in-migration to New Zealand consists of New Zealanders returning from overseas, and the number of New Zealanders overseas is correlated with the size of the resident population. Moreover, in-migration by non-New Zealanders is at least partly determined by government immigration policies, and future governments will presumably look at the size of the population when they make immigration policy.

Appendix Figure 3 - Migration rates 1961-2001
Appendix Figure 3 - Migration rates 1961-2001.

Appendix Figure 3 shows historical net migration rates. As is apparent in the figure, net immigration has fluctuated widely, with outflows roughly balancing inflows (the mean for the period shown is about 0.5 per thousand.) In contrast to fertility and mortality rates, there is no generally accepted summary index for a schedule of age-sex-specific immigration rates. (This may be one reason why demographers have traditionally used numbers rather than rates.) In the projections we therefore resorted to a somewhat awkward index: the overall net migration rates which would result if the schedule of age-sex-specific rates were applied to the New Zealand 2001 population. In the base variant, this measure is assumed to be constant at the historical average of 0.5 per thousand from 2001 to 2171; in the alternative variant it is assumed to be 0.

Age-sex-specific net migration rates were related to the summary index using the model

(16)

where is the net migration rate for age-sex group , is the net migration rate index described above, and and are coefficients for age-sex group . These coefficients were estimated from age-sex-specific migration data for the period 1996-2001.

5.4  Consumption weights

Appendix Table 1 - Consumption weights
  Base Alternative
  Male Female Male Female
0-4 342 339 279 277
5- 9  362 361 296 295
10-14 366 366 300 299
15-19 374 381 306 311
20-24 463 489 514 535
25-29 450 487 503 533
30-34 454 497 506 542
35-39 452 496 505 541
40-44 444 473 499 522
45-49 440 455 495 507
50-54 436 443 492 497
55-59 448 458 501 510
60-64 462 485 513 532
65-69 576 573 499 496
70-74 593 585 513 506
75-79 612 604 528 522
80-84 630 633 543 546
85-89 671 700 577 600
90-94 671 700 577 600
95-99 671 700 577 600
100-104 671 700 577 600
105-109 671 700 577 600
110-114 671 700 577 600
115-119 671 700 577 600
120-124 671 700 577 600
125-129 671 700 577 600

5.5  Productivity weights

Appendix Table 2 - Productivity weights
  Base Alternative
  Male Female Male Female
0-4 0 0 0 0
5- 9 0 0 0 0
10-14 0 0 0 0
15-19 159 133 119 119
20-24 542 428 403 403
25-29 900 560 670 603
30-34 1149 522 856 770
35-39 1201 602 894 805
40-44 1249 638 930 930
45-49 1274 732 949 949
50-54 1272 641 948 948
55-59 955 421 826 826
60-64 614 241 577 577
65-69 209 69 287 287
70-74 58 18 99 99
75-79 0 0 22 22
80-84 0 0 0 0
85-89 0 0 0 0
90-94 0 0 0 0
95-99 0 0 0 0
100-104 0 0 0 0
105-109 0 0 0 0
110-114 0 0 0 0
115-119 0 0 0 0
120-124 0 0 0 0
125-129 0 0 0 0
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