1. The variant projections illuminate the question of the effect of migration on population growth.
2. The components of population change (births, deaths and migration) are not independent of each other. In particular, the projected numbers of future births and deaths are themselves partly dependant on the assumed level of net migration. An understanding of the effect of migration on population change can be obtained by comparing the results of the principal and main migration variant projections with those of the "zero migration" (or natural change) variant projection. The natural change variant assumes that net migration will be zero at all ages in the future, but makes the same assumptions about fertility and mortality as the principal projection. In the analysis below, the effect of net migration on Scotland’s population in the period to 2031 is considered.
3. If annual net inward migration to Scotland were to average 4,000 per year (the long-term assumption in the principal projection) this would lead to a total net inflow of 108,000 migrants in the period between 2004 and 2031. In fact, the projected total number of migrants in this period is higher at 139,000 because the migration assumptions for the first three years are higher than the long-term projections.
4. The assumed fertility and mortality rates are the same in the principal and the zero migration (natural change) variant projection. However, because most migrants are young adults, there is a significant second generation effect with the number of migrants increasing the number of women of childbearing age and hence the future number of births. For the same reason, relatively few migrants die in the period to 2031.
5. Table 2 shows the projected components of population change in the period to 2031 in the principal projection, the high and low migration variants (which assume long-term net migration flows of +12,500 and -4,500 respectively), and the zero migration variant.
6. Table 3 shows how the projected population change is broken down between the assumed level of net migration and projected natural change.
7. In the principal projection, the population of Scotland rises by 48,000 by 2031 due to "extra" natural change due to migration and under the high migration variant this increases to 96,000.