Actuarial Note 148
The chart illustrates how immigration flow is modeled. A big circle represents the Social Security area (SSA) population. Inside the big circle are two disjoint smaller circles, one circle represents the other-immigrant population and the other circle represents the legal-immigrant population. The model shows annual flows into and out of the circles.
Flowing into the legal-immigrant population are legal permanent residents (LPRs). The assumed annual numbers of LPRs flowing into this population are 500,000 from outside the SSA population and 500,000 from the other-immigrant population. In addition, 250,000 persons are assumed to annually leave the SSA population from either the legal-immigrant population or the non-immigrant population.
Flowing into the other-immigrant population are other immigrants from outside the SSA population, assumed to be 1.5 million per year. The annual number of persons who leave the other-immigrant population consists of the 500,000 that become LPRs and a varying number, which averages about 700,000 per year, who leave the SSA population.