Assumptions about lower and higher levels for future mortality help us assess the sensitivity of future population change to mortality variations. We use the same lower and higher mortality assumptions as are used for the Census Bureau's 1995 national population projections. For the low, medium, and high mortality assumptions, we assume the same levels of mortality, by sex and for each race and Hispanic group, for 1995. For 2050, we assume the mortality levels shown in Appendix 3.B: Table 3.B1.
We make five different immigration assumptions about net immigration—termed zero, low, medium, high, and very high—in order: 0, 410,000, 820,000, 1,230,000, and 1,640,000. The medium assumption of 820,000 is close to the average for the period 1990-95 and includes the assumption of about 225,000 net annual illegal immigrants. The zero assumption implies both zero immigrants and zero emigrants, providing a context for discussing the overall net impact of immigration on population change. The low assumption of 410,000 assumes a decline to immigration levels that are close to net immigration during the 1980s. The high assumption represents possible expanded legal immigration through