	Introduction

Social Security Disability Insurance (SSDI) is a federal social insurance program that provides monthly cash benefits to non-elderly disabled workers and their eligible dependents provided the worker paid into the system for a sufficient number of years and is determined to be unable to perform substantial work because of a qualifying disability. In the past three decades, the total number of disabled-worker beneficiaries continually increased from 2.7 million in 1985 to 9.0 million in 2014 and then started to decline to approximately 8.7 million in December 2017. Multiple factors have contributed to the change in the number of SSDI beneficiaries over time. Changes in the Demographic Characteristics of the Insured Population

The number of SSDI disabled-worker beneficiaries depends in part on the size of the working-age population who are disability insured—the workers who have paid into the Social Security system for a sufficient number of years. However, because the share of women in the workforce was no longer increasing and the baby boom generation (people born between 1946 and 1964) was aging out of the disability insurance program, the growth in the insured population slowed after 2007. Female Labor Force Participation

Some studies have shown that increased eligibility for the SSDI program and the rising incidence of disability among women played an important role in disability benefit receipt during the 1980s and the 1990s. Some experts attribute the increase in beneficiaries to increased labor force participation of women, which resulted in more women becoming potentially eligible for SSDI. During the same time, the incidence rate for men has been relatively steady after adjusting for the population age distribution and the business cycle. The Change in Age Distribution of the Population

Another factor that contributes to the trends in SSDI enrollment is the aging of the workforce. Some argue that as baby boomers reached their peak disability-claiming years (usually considered between age 50 and FRA), the number of disability beneficiaries rose, and as baby boomers convert from disability benefits to retirement benefits and are replaced by lower-birth-rate cohorts in the peak disability-receiving ages, the disability enrollment rates will likely fall. The effect of the ACA on SSDI enrollment is not yet clear. These phenomena are likely to result in a further increase in SSDI rolls and program spending. 1. The opportunities for employment make working more attractive than disability benefits for people who could qualify for SSDI. 2. The lower-birth-rate cohorts (people born after 1964) started to enter peak disability-claiming years (usually considered ages 50 to FRA) in 2015, replacing the larger baby boom population. 3. Availability of the Affordable Care Act (ACA) . The nationwide effect of the ACA on disability benefit receipt is still unclear. 4. Decline in the allowance rate . In addition to the factors contributing to a decline in SSDI applications and awards, some others may have the opposite effect of pushing disability benefit receipt upward. Some of those factors may include the increase in the FRA, the growth in applications from low-wage workers, and higher incidence rates among young applicants resulting from an expansion of SSDI eligibility rules. As the relatively large baby boomer population reaches its FRA (gradually increased from 65 to 66) between 2012 and 2031, there is expected to be a growing proportion of disabled workers who terminate disability benefits due to the attainment of FRA. The potential increase in the number of terminations may slow down due to the scheduled increase in the FRA from 66 to 67 between 2020 and 2027, which will result in fewer disabled workers exiting the SSDI program due to the attainment of FRA. Availability of the ACA . Some factors may work in the opposite direction to decrease disability terminations.
The Social Security Disability Insurance (SSDI) program pays cash benefits to non-elderly workers and their dependents provided that the workers have paid into the Social Security system for a sufficient number of years and are determined to be unable to continue performing substantial work because of a qualifying disability. The total number of disabled-worker beneficiaries was approximately 2.7 million in 1985, peaked at approximately 9.0 million in 2014, and then declined over the last three years by nearly 0.3 million. In December 2017, 8.7 million disabled workers received SSDI benefits.
Multiple factors have contributed to the growth in the SSDI enrollment between 1985 and 2014. Some of the main factors are (1) the increased eligibility and rising disability incidence among women, (2) the attainment of peak disability-claiming years (between age 50 and full retirement age) among baby boomers (people born between 1946 and 1964), (3) the increase in full retirement age (FRA) from 65 to 66, (4) fewer job opportunities during economic recessions, and (5) the legislative reform that expanded the eligibility standard in SSDI.
Some factors may have prolonged effects on SSDI benefit receipt. For example, the increase in the FRA from 65 to 66 has resulted in a larger proportion of SSDI beneficiaries who are ages 65 and older, and this proportion is likely to increase further as the FRA increases from 66 to 67 between 2020 and 2027. Another example is the consequence of the expansion in the eligibility criteria, which has resulted in more than half of the disabled-worker beneficiaries being enrolled into the program based on mental disorders or musculoskeletal disorders (typically back pain or arthritis). This trend is likely to persist in the future.
However, some of the effects on the growth in SSDI enrollment are likely to diminish over time. For example, the rise in labor force participation among women resulted in more women becoming eligible for SSDI benefits during the 1980s and the 1990s, but its positive effect on SSDI rolls became smaller as the female labor force participation rate stabilized and the disability incidence rate of women approached that of men.
In addition, some factors may have started to work in opposite directions. One example is the change in age distribution of the population. As the baby boomers reach their FRA (gradually increased from 65 to 66) between 2012 and 2031, there is expected to be a growing proportion of disabled workers who terminate disability benefits due to the attainment of FRA. About the same time, the lower-birth-rate cohorts (people born after 1964) started to enter peak disability-claiming years in 2015, which would likely reduce the size of the insured population between age 50 and the FRA and, consequently, result in a lower number of disability applications. Another example is the availability of more jobs during the post-Great Recession period. The increasing opportunity in employment may have made working more attractive than disability benefits for people who could qualify for SSDI, thus reducing the disability applications and awards after 2010. These factors are likely to contribute to a decline in the number of disabled-worker beneficiaries.
In addition to the change in the population age distribution and the availability of jobs in the market, some other factors may also be acting to decrease SSDI rolls in the recent three years. These factors are likely to include the prevalence of the Affordable Care Act (ACA) and the decline in the allowance rate (i.e., the share of applicants who are awarded disability benefits). The nationwide effects of the ACA on disability benefit receipt and the cause of the decreasing allowance rate are as yet unclear.