2002 OASDI Trustees Report

V. ASSUMPTIONS AND METHODS UNDERLYING
ACTUARIAL ESTIMATES

The future income and outgo of the OASDI program will depend on many demographic, economic, and program-specific factors. Trust fund income will depend on how these factors affect the size and composition of the working population and the level and distribution of earnings. Similarly, trust fund outgo will depend on how these factors affect the size and composition of the beneficiary population and the general level of benefits.

Basic assumptions are developed for several of these factors based on analysis of historical trends and conditions, and on expected future conditions. These include fertility, mortality, immigration, marriage, divorce, productivity, inflation, average earnings, unemployment, retirement, and disability incidence and termination. Other factors are projected using methods that reflect historical and expected future relationships to the basic assumptions. These include total population, life expectancy, labor force, gross domestic product, interest rates, and a myriad of program-specific factors. It should be noted that all factors included in any consistent set of assumptions are interrelated directly or indirectly. It is also important to note that these interrelationships can and do change over time.

The assumptions and methods used in this report are reexamined each year in light of recent experience and new information about future conditions, and are revised if warranted.

Because projections of these factors and their interrelationships are inherently uncertain, estimates are shown in this report on the basis of three plausible sets of assumptions, designated as intermediate (alternative II), low cost (alternative I), and high cost (alternative III). The intermediate set, represents the Board's best estimate of the future course of the population and the economy. In terms of the net effect on the status of the OASDI program, the low cost is the most optimistic, and the high cost is the most pessimistic.

Although these three sets of demographic and economic assumptions have been developed using the best available information, the resulting estimates should be interpreted with care. The estimates are not intended to be specific predictions of the future financial status of the OASDI program, but rather, they are intended to be indicators of the expected trend and a reasonable range of future income and outgo, under a variety of plausible demographic and economic conditions.

The values for each of the demographic, economic, and program-specific factors are assumed to move from recently experienced levels or trends, toward long-range ultimate values over the next 5 to 30 years. The ultimate values assumed after the first 5 to 30 years for both the demographic and the economic factors are intended to represent average experience or growth rates. Actual future values will exhibit fluctuations or cyclical patterns, as in the past.

The following sections discuss in abbreviated form the various assumptions and methods required to make the estimates of trust fund financial status which are the heart of this report.¹ There are, of course, many interrelationships among these factors that make a sequential presentation somewhat misleading. Nevertheless, the following sections roughly follow the order used in building the trust fund estimates presented in chapter IV.

A. DEMOGRAPHIC ASSUMPTIONS AND METHODS

The principal demographic assumptions relating to fertility, mortality, and net immigration for the three alternatives are shown in table V.A1. The rationales for selecting these assumptions are discussed in the following three sections.

1. Fertility Assumptions

Fertility (birth rate) assumptions are developed by single year of age, from 14 to 49. They are applied to the total number of women in the population at each age, for all marital statuses.

Historically, fertility rates in the United States have fluctuated widely. The total fertility rate² decreased from 3.3 children per woman after World War I to 2.1 during the Great Depression, rose to 3.7 in 1957, and then fell to 1.7 in 1976. After 1976, the total fertility rate began to rise again, reaching a level of 2.07 for 1991. Since then, the total fertility rate has remained fairly stable.

These variations in fertility rates have resulted from changes in many factors, including social attitudes, economic conditions, and the use of birth-control methods. Future fertility rates may be expected to remain close to recent levels. The recent historical and projected trends in certain population characteristics are consistent with a continued relatively low fertility rate. These trends include the rising percentages of women who have never married, of women who are divorced, and of young women who are in the labor force. Based on consideration of these factors, ultimate total fertility rates of 2.2, 1.95, and 1.7 children per woman were selected for the low cost, intermediate, and high cost assumptions, respectively. For each alternative, the total fertility rate is assumed to gradually trend from the estimated level of 2.13 for 2000, reaching the selected ultimate level for 2026 and later.

2. Mortality Assumptions

Mortality (death rate) assumptions are developed by single year of age, sex, and cause of death.

Over the last century, death rates in the United States have declined substantially, but at varying rates. Historical rates (for years 1900-99) used in preparing this report were calculated for ages below 65 (and for all ages prior to 1968) using data from the National Center for Health Statistics (NCHS).³ For ages 65 and over, Medicare final data were used for years 1968 through 1999. Also used are death rates by cause of death produced by the NCHS for years 1979-99.

The total age-sex-adjusted death rate⁴ declined at an average rate⁵ of 1.10 percent per year between 1900 and 1999. Between 1979 and 1999, the period for which death rates are analyzed by cause, the total age-sex-adjusted death rate (for all causes combined) declined at an average rate of 0.70 percent per year.

Historical death rates have declined more slowly for older ages than for the rest of the population. The age-sex-adjusted death rate for ages 65 and over declined at an average rate of 0.73 percent per year between 1900 and 1999. Between 1979 and 1999 the age-sex-adjusted death rate for these ages declined at an average annual rate of 0.42 percent.

Reductions in death rates have resulted from many factors, including increased medical knowledge and availability of health-care services, and improvements in sanitation and nutrition. Based on consideration of the expected rate of future progress in these and other areas, three alternative sets of ultimate annual percentage reductions in central death rates by age, sex, and cause of death were selected for 2026 and later. The intermediate set, which is used for alternative II, is considered to be the most likely to occur. The average annual percentage reductions used for alternative I are generally smaller than those for alternative II, while those used for alternative III are generally greater.

After 1999, the reductions in central death rates for alternative II are assumed to change rapidly from the average annual reductions by age, sex, and cause of death observed between 1979 and 1999, to the ultimate annual percentage reductions by age, sex, and cause of death assumed for 2026 and later. The reductions in death rates under alternatives I and III are also assumed to change rapidly to their ultimate levels, but start from levels which are, respectively, 50 or 150 percent of the average annual reductions observed between 1979 and 1999.

Projections of age-sex-adjusted death rates are presented in table V.A1 for the total (all ages), for under age 65, and for ages 65 and over. For the first few years of the projection period, death rates for the total are slightly higher than those death rates in last year's report. New data for 1999 resulted in the estimation of starting mortality rates that are higher than those in last year's report. However, within the first 20 years, projected total death rates become smaller than those in last year's report because of revised methods that result in faster reduction during the early years of the projection period. Age-sex- adjusted mortality continues to decline faster than in last year's report because of these revised methods, even though the ultimate rates of decline in cause-specific mortality are the same as those used in last year's report.

After adjustment for changes in the age-sex distribution of the population, the resulting total death rates are projected to decline at ultimate average annual rates of about 0.35 percent, 0.73 percent, and 1.29 percent between 2026 and 2076 for alternatives I, II, and III, respectively. In keeping with the patterns observed in the historical data, future rates of decline are assumed to be greater for younger ages than for older ages, but to a lesser degree than in the past. Accordingly, age-sex-adjusted death rates for ages 65 and over are projected to decline at average annual rates of about 0.30 percent, 0.70 percent, and 1.23 percent between 2026 and 2076 for alternatives I, II, and III, respectively.

There is a wide range of opinion among experts on the likely rate of future decline in death rates. For example, the 1999 Technical Panel on Assumptions and Methods appointed by the Social Security Advisory Board believed that ultimate rates of decline in mortality will be higher than the rates of decline assumed for the intermediate projections in this report. Others believe that biological and social factors may slow future rates of decline in mortality. Evolving mortality trends and developments in health care and life style will be closely monitored to determine what further modifications to the assumed ultimate rates of decline in mortality may be warranted for future reports.

3. Immigration Assumptions

Legal immigration increased after World War II to around 300,000 persons per year and remained around that level until shortly after 1960. With the Immigration Act of 1965 and other related changes, annual legal immigration increased to about 400,000 and remained fairly stable until 1977. Between 1977 and 1990, legal immigration once again increased, averaging about 580,000 ⁶ per year. The Immigration Act of 1990, which took effect in fiscal year 1992, restructured the immigration categories and increased significantly the number of immigrants who may legally enter the United States. Legal immigration averaged about 760,000 ⁶ persons per year during the period 1990 through 1999. The number of legal immigrants in 2000 is estimated to be about 850,000 persons.

For calendar year 2000, net legal immigration (after considering emigration) is estimated to be about 640,000 persons. Net other-than-legal immigration is estimated to be 300,000 persons. For calendar year 2001, net legal immigration is estimated to be 620,000 persons and net other-than-legal is estimated to be 300,000 persons.

The total level of net immigration (legal and other-than-legal, combined) under the intermediate projection is assumed to be 900,000 persons⁷ in 2002 and for each year afterward. For the low cost assumptions, net immigration is assumed to rise from a level of 1,140,000 persons in 2002 to an ultimate level of 1,210,000 persons⁸ for each year 2003 and later. Under the high cost assumptions, net immigration is assumed to be 718,000 persons in 2002, and 655,000 persons⁹ for each year after 2002.

The levels of net immigration during 2001 to 2003 are slightly different from those used in last year's report. The ultimate levels of net immigration are the same as those assumed in last year's report.

4. Total Population Estimates

Combining the above assumptions for future fertility, mortality, and net immigration with assumptions on marriage and divorce based on data from NCHS, projections were made of the population in the Social Security area by age, sex, and marital status as of January 1 of each year 2001 through 2080. The starting Social Security area population for January 1, 2000, uses as a basis the Census Bureau's estimate of the residents of the 50 States and D.C., and U.S. Armed Forces overseas. This base estimate is adjusted for net census undercount and increased for other U.S. citizens living abroad (including residents of U.S. territories) and for non-citizens living abroad who are insured for Social Security benefits. This starting population was then projected using assumed rates of birth, death, marriage and divorce, and assumed levels of migration.

Table V.A2 shows the projected population as of July 1 by broad age group, for the three alternatives. Also shown are tabulated aged and total dependency ratios (see table footnotes for definitions).

Note: Totals do not necessarily equal the sums of rounded components.

5. Life Expectancy Estimates

Life expectancy, or average remaining number of years expected prior to death, is a useful analytical concept. Life expectancy is calculated in two different forms, for two separate purposes.

Period life expectancy is calculated for a given year using the actual or expected death rates at each age for that year. It is a useful summary statistic for illustrating the overall level of the death rates experienced in a single year. It is thus closely related to the age-sex-adjusted death rate that is discussed in section V.A.2. Period life expectancy for a particular year may be viewed as the expected remaining life at a selected age only if it is assumed that there is no change in death rates after that year.

Cohort life expectancy truly answers the question "What is the expected average remaining lifetime for an individual at a selected age in a given year?" Cohort life expectancies are calculated using death rates not from a single year, but from the series of years in which the individual will actually reach each succeeding age if he or she survives.

Tables V.A3 and V.A4 present historical and projected life expectancies calculated on both period and cohort bases. Cohort life expectancies are somewhat greater than period life expectancies for the same year. This is because death rates for any given age tend to decline as time passes and the cohort grows older.