2019 OASDI Trustees Report

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V. ASSUMPTIONS AND METHODS UNDERLYING
ACTUARIAL ESTIMATES
The future income and cost 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 as well as the level and distribution of earnings. Similarly, program cost will depend on how these factors affect the size and composition of the beneficiary population as well as the general level of benefits.
The Trustees make basic assumptions for several of these factors based on analysis of historical trends, historical conditions, and expected future conditions. These factors include fertility, mortality, immigration, marriage, divorce, productivity, inflation, average earnings, unemployment, real interest rates, and disability incidence and termination. Other factors depend on these basic assumptions. These other, often interdependent, factors include total population, life expectancy, labor force participation, gross domestic product, and program-specific factors. Each year the Trustees reexamine these assumptions and methods in light of new information and make appropriate revisions. The assumptions for this report were selected by the middle of January 2019.
Future levels of these factors and their interrelationships are inherently uncertain. To address these uncertainties, this report uses three sets of assumptions, designated as intermediate (alternative II), low-cost (alternative I), and high-cost (alternative III). The intermediate set represents the Trustees’ best estimate of the future course of the population and the economy. With regard to the net effect on the actuarial status of the OASDI program, the low-cost set is more optimistic and the high-cost set is more pessimistic. The low-cost and high-cost sets of assumptions reflect significant potential changes in the interrelationships among factors, as well as changes in the values for individual factors.
While it is unlikely that all of the factors and interactions will differ in the specified directions from the intermediate values, many combinations of individual differences in the factors could have a similar overall effect. Outcomes with overall long-range cost as low as the low-cost scenario or as high as the high-cost scenario are very unlikely. This report also includes a section on sensitivity analysis, where factors are changed one at a time (see appendix D), and a section on stochastic projections, which provides a probability distribution of possible future outcomes, with most of the key factors being varied around the intermediate alternative (see appendix E).
Readers should interpret with care the estimates based on the three sets of alternative assumptions. These estimates are not specific predictions of the future financial status of the OASDI program. Rather, they provide a reasonable range of future income and cost.
All of the key demographic, economic, and program-specific assumptions reach their long-range ultimate values within the next 25 years. For extrapolations beyond the 75‑year long-range period, the ultimate levels or trends reached by the end of the 75‑year period remain unchanged. The assumed ultimate values represent average annual experience or growth rates. Actual future values will exhibit fluctuations or cyclical patterns, as in the past.
The following sections briefly discuss the various assumptions and methods used in making the estimates of trust fund actuarial status, which are the focus of this report.1 There are, of course, many interrelationships among these factors that are important but are beyond the scope of this discussion.
A. DEMOGRAPHIC ASSUMPTIONS AND METHODS
This section of the report provides a brief overview of the demographic historical data and the assumptions used for the projections.
1. Fertility Assumptions
Birth rates by single year of age, for women aged 14 to 49,2 are the basis for the fertility assumptions. These rates apply to the total number of women, across all marital statuses, in the midyear population at each age. Table V.A1 displays the historical and projected total fertility rates.3
Historically, birth rates in the United States have fluctuated widely. The total fertility rate decreased from 3.31 children per woman at the end of World War I (1918) to 2.15 during the Great Depression (1936). After 1936, the total fertility rate rose to 3.68 in 1957 and then fell to 1.74 by 1976. After 1976, the total fertility rate rose above 2.00 by 1990, where it generally remained through 2009, but dropped below 1.90 for 2011 through 2017 and is estimated to be 1.74 in 2018.
These variations in the total fertility rate resulted from changes in many factors, including social attitudes, economic conditions, birth-control practices, and the racial/ethnic composition of the population. Since the baby-boom era (1946-65), women have had higher educational attainment, higher labor force participation, an older average age at first marriage, a higher propensity to remain unmarried, and higher rates of divorce. All of these factors are consistent with continued lower total fertility rates than those experienced during the baby-boom era. Based on consideration of these factors, the Trustees expect the total fertility rate for future years to remain relatively close to the average level since the end of the baby-boom era. The assumed ultimate total fertility rates are 2.20, 2.00, and 1.80 children per woman for the low-cost, intermediate, and high-cost assumptions, respectively. These ultimate rates are unchanged from last year’s report.
For the intermediate assumptions, the projected total fertility rate gradually increases from 2018 through the year the ultimate value is reached (2027) with somewhat more rapid increases in the middle of the 2018-2027 period. The assumed low-cost and high-cost total fertility rates trend away from the intermediate path and reach the ultimate values in 2027 and 2024, respectively.
2. Mortality Assumptions
For the projections in this year’s report, ultimate average annual percentage reductions in future mortality rates were assumed by age group and cause of death. These assumptions were then used to estimate future central death rates by age group, sex, and cause of death. From these estimated central death rates, probabilities of death by single year of age and sex were calculated.
Historical death rates were calculated for years 1900 through 2016 for ages below 65 (and for all ages for years prior to 1968) using data from the National Center for Health Statistics (NCHS).4 For ages 65 and over, final Medicare data on deaths for years 1968 through 2015 and preliminary data for 2016 and 2017 were used.5 Death rates by cause of death were produced for all ages for years 1979‑2016 using data from the NCHS.
The total age-sex-adjusted death rate6 declined at an average annual rate of 1.03 percent between 1900 and 2016. Between 1979 and 2016, the period for which death rates were analyzed by cause, the total age-sex-adjusted death rate, for all causes combined, declined at an average rate of 0.87 percent per year.
Death rates have declined substantially in the U.S. since 1900, with rapid declines over some periods and slow or no improvement over the other periods. Many factors are responsible for historical reductions in death rates, including medical advances, increased availability of health-care services, and improvements in sanitation and nutrition. Historical death rates generally declined more slowly for older ages and more rapidly for children and infants than for the rest of the population. Between 1900 and 2016, the age-sex-adjusted death rate declined at an average rate of 0.78 percent per year for ages 65 and over, and 3.00 percent per year for ages under 15.
Mortality assumptions differ for the low-cost, intermediate, and high-cost scenarios. Throughout the projection, the low-cost scenario contains annual percentage reductions that are smaller than those in the intermediate scenario, while those in the high-cost scenario are larger. The ultimate annual percentage reductions for each of the three alternatives are the same as those in last year’s report.
The trends in the annual reductions in central death rates were calculated for the period from 2006 to 2016 for NCHS data, and 2007 to 2017 for Medicare data, by age group, sex, and cause of death.7 These trends are the starting reductions for alternative II. For alternatives I and III, 50 and 150 percent of the starting reductions are used, respectively. These annual reductions, by alternative, are assumed to transition rapidly from the starting reductions until they reach the ultimate annual percentage reductions assumed for 2043 and later.
Table V.A1 contains historical and projected age-sex-adjusted death rates for the total population (all ages), for ages under 65, and for ages 65 and over. Age-sex adjustment eliminates the effect of a changing distribution of population by age and sex, allowing the pure effects of changes in death rates to be observed. Under the intermediate assumptions, projected age-sex-adjusted death rates are, in general, slightly higher than the death rates in last year’s report for both the age group under 65 and the age group 65 and over. These changes primarily result from incorporating more recent historical data, which continue to show low rates of improvement.
The projected average annual rate of decline for the total age-sex-adjusted death rate is about 0.41 percent, 0.77 percent, and 1.16 percent between 2018 and 2093 for alternatives I, II, and III, respectively. In keeping with the patterns observed in the historical data, the assumed future rates of decline are greater for younger ages than for older ages, but to a substantially lesser degree than in the past. Accordingly, the projected age-sex-adjusted death rates for ages 65 and over decline at average annual rates of about 0.37 percent, 0.68 percent, and 1.02 percent between 2018 and 2093 for alternatives I, II, and III, respectively. The projected age-sex-adjusted death rates for ages under 15 decline at average annual rates of about 0.80 percent, 1.58 percent, and 2.57 percent between 2018 and 2093 for alternatives I, II, and III, respectively.
Demographers express a wide range of views on the likely rate of future decline in death rates. For example, some believe that the long-standing historical tendency for mortality to decline more slowly at the oldest ages will cease in the future. Others believe that biological factors, social factors, and limitations on health care spending may slow future rates of decline in mortality.
.
Table V.A1.—Fertility and Mortality Assumptions,a
Calendar Years 1940-2095 
Total
fertility
rateb
Age-sex-adjusted death rate c
per 100,000
d 808.2
260.5
d 4,460.0
d  802.7
d 250.6
d 4,483.6
e 1.74
e 791.8
e 249.3
e 4,408.3

a
This table contains basic assumptions along with key summary values that are derived from basic assumptions.

b
The total fertility rate for any year is the average number of children that would be born to a woman if she were to experience, at each age of her life, the birth rate observed in, or assumed for, the selected year, and if she were to survive the entire childbearing period.

c
Based on the enumerated total population as of April 1, 2010, if that population were to experience the death rates by age and sex observed in, or assumed for, the selected year.

d
Estimated.

e
Estimated, intermediate alternative.

3. Immigration Assumptions
Projections of the total Social Security area population reflect assumptions for annual immigration flows. For this report, four categories of immigration flows are used:
Lawful permanent resident (LPR) immigration: Persons who enter the Social Security area and are granted LPR status, or who are already in the Social Security area and adjust their status to become LPRs.8
Net LPR immigration is the difference between LPR immigration and legal emigration. Net other-than-LPR immigration is the difference between other-than-LPR immigration and other-than-LPR emigration. Total net immigration refers to the sum of net LPR immigration and net other-than-LPR immigration.
Immigration assumptions differ for the low-cost, intermediate, and high-cost scenarios. The low-cost scenario includes higher annual net immigration and the high-cost scenario includes lower annual net immigration. Table V.A2 contains historical and projected levels of various immigration flows.
LPR immigration has increased significantly since World War II, due to various factors and legislative changes, including the Immigration Act of 1965 and the Immigration Act of 1990.
For the intermediate alternative, the ultimate level of annual LPR immigration, which includes residents who adjust their status to become LPRs, is assumed to be 1,050,000 persons for 2020 and later. For alternative I, ultimate annual LPR immigration is assumed to be 1,250,000 persons for 2020 and later, and for alternative III, ultimate annual LPR immigration is assumed to be 850,000 persons for 2020 and later. The ultimate levels of LPR immigration are unchanged from last year’s report.
The assumed ratios of annual legal emigration to LPR immigration are 20, 25, and 30 percent for alternatives I, II, and III, respectively. This range is consistent with the limited historical data for legal emigration from the Social Security area. These ratios are unchanged from last year’s report. Under the intermediate alternative, by combining the ultimate annual LPR immigration and legal emigration assumptions, ultimate annual net LPR immigration is about 788,000 persons. For the low-cost and high-cost scenarios, ultimate annual net LPR immigration is 1,000,000 persons and 595,000 persons, respectively.
The estimated number of other-than-LPR immigrants residing in the Social Security area and the annual level of other-than-LPR immigration have been affected significantly by the most recent recession. Although net other-than-LPR immigration was greatly reduced during the economic downturn, it has begun to rise since then. Under the intermediate assumptions, annual other-than-LPR immigration is expected to continue increasing, reflecting a continued recovery from levels experienced during the recession. In last year’s report, other-than-LPR immigration under the intermediate assumptions was projected to increase to a peak level in 2018 and then decrease to the ultimate level in 2022, based on the expectation that the continuing economic recovery would result in other-than-LPR immigration levels that would make up for the lower levels experienced during the recession. However, recent other-than-LPR immigration levels have not followed this pattern. Under the intermediate assumptions for this year’s report, other-than-LPR immigration is assumed to attain the ultimate level in 2019. The ultimate levels of other-than-LPR immigration are unchanged from last year’s report: 1,350,000 persons for alternative II, 1,650,000 persons for alternative I, and 1,050,000 persons for alternative III.
Emigration from the other-than-LPR immigrant population includes those who leave the Social Security area and those who adjust their status to become LPRs. This other-than-LPR immigrant population is highly mobile and far more likely to leave the Social Security area than is the citizen or LPR population. However, as other-than-LPR immigrants stay in the country for longer periods of time, they generally become less likely to leave the country.
Under the intermediate assumptions, the total annual number of other-than-LPR immigrants who leave the Social Security area averages about 422,000 through the 75‑year projection period. In addition, the ultimate annual number of other-than-LPR immigrants who adjust status to become LPRs is assumed to be 450,000 for the intermediate assumptions. For the low-cost and high-cost scenarios, the total annual number of other-than-LPR emigrants averages about 496,000 and 346,000, respectively, through the 75‑year projection period. The ultimate annual number of people adjusting status to LPR status is assumed to be 550,000 persons and 350,000 persons, for the low-cost and high-cost scenarios, respectively. The ultimate annual number of people adjusting status to become LPRs is one-third as large as the assumed ultimate annual number of the other-than-LPR immigrants entering the Social Security area, and is unchanged from last year’s report for all three sets of assumptions.
Under the assumptions described above, the projected size of the other-than-LPR immigrant population grows substantially. This growth reflects the excess of annual immigration over the combined annual numbers of emigrants (including adjustments of status) and deaths that occur within the other-than-LPR immigrant population.
Under the intermediate assumptions, projected net other-than-LPR immigration gradually decreases over time. Because the projected number of other-than-LPR immigrants leaving the Social Security area is based on rates of departure, an increase in the number of other-than-LPR immigrants residing in the Social Security area results in an increase in the number who emigrate out of the area. All other components of other-than-LPR immigration and emigration are assumed to be stable after 2019, and thus do not contribute toward any change in annual net other-than-LPR immigration. Under the intermediate assumptions, the projected average annual level of net other-than-LPR immigration over the 75-year projection period is about 478,000 persons. For the low-cost and high-cost assumptions, projected average annual net other-than-LPR immigration is about 601,000 persons and 354,000 persons, respectively.
The projected average annual level of total net immigration (LPR and other-than-LPR, combined) is about 1,265,000 persons per year during the 75-year projection period under the intermediate assumptions. For the low-cost and high-cost assumptions, projected average annual total net immigration is about 1,601,000 persons and 949,000 persons, respectively.
Demographers express a wide range of views about the future course of immigration for the United States. Some believe that net immigration will increase substantially in the future. Others believe that potential immigrants may be increasingly attracted to other countries, that the number of potential immigrants may be lower due to lower birth rates in many countries, or that changes in the law or enforcement of the law will reduce immigration.
Table V.A2.—Immigration Assumptions,a Calendar Years 1940-2095 
Other-than-LPR immigrationb
Adjustments
of statusc d
e724
e282
e403
e845
f1,250
e237
e403
f610
f1,456
f620
f268
f450
f803
f1,300
f249
f450
f601
f1,404

a
This table contains basic assumptions along with key summary values that are derived from basic assumptions.

b
Historical other-than-LPR immigration and emigration estimates depend on a residual method. The Office of the Chief Actuary developed these estimates, as well as the resulting other-than-LPR January 1 stock estimates, for years through 2000. For years 2001 and later, the residual method uses stock estimates. For 2001 through 2004, the stock is set to values that linearly grade from the 2000 stock estimate to the DHS 2005 stock estimate. For 2005 through 2012, stock estimates come from DHS. For 2013 through 2016, stock estimates are developed by the Office of the Chief Actuary, based on the same methods used by DHS.

c
Estimates do not include persons who attained LPR status under the special one-time provisions of the Immigration Reform and Control Act of 1986.

d
Adjustments of status are a positive for net LPR immigration and a negative for net other-than-LPR immigration.

e
Estimated.

f
Estimated, intermediate alternative.
Note: Totals do not necessarily equal the sums of rounded components.

4. Total Population Estimates
The starting Social Security area population for December 31, 2016, is derived from the Census Bureau’s estimate of the residents of the 50 States and D.C. and U.S. Armed Forces overseas. Adjustments are made to reflect mortality assumptions for the aged population since 2010 that are consistent with Medicare and Social Security data, net immigration assumptions for the aged population since 2010, estimates of the net undercount in the 2010 census, inclusion of U.S. citizens living abroad (including residents of U.S. territories), and inclusion of non-citizens living abroad who are insured for Social Security benefits. The Office of the Chief Actuary projects the population in the Social Security area by age, sex, and marital status for December 31 of each year from 2017 through 2095 by combining the assumptions for future fertility, mortality, and immigration with assumptions for marriage and divorce. Previous sections of this chapter present the assumptions for future fertility, mortality, and immigration. Assumptions for future rates of marriage and divorce reflect historical data from the National Center for Health Statistics, the Census Bureau, and selected individual States.
This report presents a July 1 (i.e., midyear) population for each year, which is derived from surrounding December populations. Table V.A3 shows the historical and projected population for July 1 by broad age group, for the three alternatives. It also shows the aged and total dependency ratios (see table footnotes for definitions).
Aged a
Total b
2016 c

a
Ratio of the population at ages 65 and over to the population at ages 20-64.

b
Ratio of the population at ages 65 and over and the population under age 20 to the population at ages 20‑64.

c
Estimated.

d
Estimated, intermediate alternative.

Notes:
1. Historical data are subject to revision.
2. Totals do not necessarily equal the sums of rounded components.
5. Life Expectancy Estimates
Life expectancy, or the average remaining number of years expected prior to death, is an additional way to summarize the Trustees’ mortality assumptions. This report includes life expectancy in two different forms (period and cohort), which are useful for two separate purposes.
Cohort life expectancy does not incorporate death rates for a single year, but for the series of years in which the individual will actually reach each succeeding age if he or she survives. Cohort life expectancy provides an individual’s expected average remaining lifetime at a selected age in a given year, using actual or expected future death rates. Table V.A5 presents historical and projected life expectancy calculated on a cohort basis. Cohort life expectancy is somewhat greater than period life expectancy for a given year because: (1) death rates at any age tend to decline over time; and (2) cohort life expectancy uses death rates from future years, while period life expectancy uses death rates only from the given year.
Life expectancy at a given age reflects death rates at that and all older ages. Period life expectancy is somewhat related to the age-sex-adjusted death rate discussed in section V.A.2. However, life expectancy places far greater weight on death rates at relatively younger ages than those at relatively older ages. Therefore, changes in death rates at younger ages have far greater effects in changing life expectancy over time. It is important to keep this concept in mind when considering trends in life expectancy.
2014   
2015   
2016 b
2018 c

a
The period life expectancy at a given age for a given year is the average remaining number of years expected prior to death for a person at that exact age, born on January 1, using the mortality rates for that year over the course of his or her remaining life.

b
Estimated.

c
Estimated, intermediate alternative.

At birthb
At age 65c

a
The cohort life expectancy at a given age for a given year is the average remaining number of years expected prior to death for a person at that exact age, born on January 1, using the mortality rates for the series of years in which the individual will actually reach each succeeding age if he or she survives.

b
Cohort life expectancy at birth for those born in the calendar year is based on a combination of actual, estimated, and projected death rates for birth years 1940 through 2016. For birth years after 2016, these values depend on estimated and projected death rates.

c
Age 65 cohort life expectancy for those attaining age 65 in calendar years 1940 though 2015 depends on actual death rates or on a combination of actual, estimated, and projected death rates. After 2015, these values depend on estimated and projected death rates.


1
Actuarial Studies published by the Office of the Chief Actuary, Social Security Administration, contain further details about the assumptions, methods, and actuarial estimates. A complete list of available studies may be found at www.ssa.gov/OACT/NOTES/actstud.html. To obtain copies of such studies or of this report, please submit a request at www.ssa.gov/OACT/request.html. This entire report, along with supplemental year-by-year tables and additional documentation on assumptions and methods, may be found at www.ssa.gov/OACT/TR/2019/.

2
Birth rates at age 14 include births to women aged 14 and under, and birth rates at age 49 include births to women aged 49 and over.

3
The total fertility rate may be interpreted as the average number of children that would be born to a woman if she were to experience, at each age of her life, the birth rate observed in, or assumed for, a specified year, and if she were to survive the entire childbearing period. A rate of about 2.1 would ultimately result in a nearly constant population if immigration and emigration were both zero, and if death rates were to remain at current levels.

4
These rates reflect NCHS data on deaths and Census estimates of population.

5
These rates reflect Medicare data on deaths and enrollments.

6
Based on the enumerated total population as of April 1, 2010, if that population were to experience the death rates by age and sex for the selected year.

7
Cause of death is only available for the NCHS data.

8
Persons who enter the country with legal visas but without LPR status, such as temporary foreign workers and students, are not included in the “LPR immigration” category.


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