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Health Tracking

TRENDS

Are The Young Becoming More Disabled?

Abstract

 
This paper investigates trends in disability in the U.S. population, particularly among people under age fifty. Even as the elderly have become less disabled, reported disability has risen for younger Americans, especially those ages 30–49. We suggest some possible explanations for rising disability levels, such as obesity, technological advances in medicine, and changing disability insurance laws. Obesity and its attendant disorders seem particularly associated with these trends, although the data are not definitive. Whatever its sources, rising disability among the young could have adverse consequences for public programs such as disability insurance, Medicare, and Medicaid.

Given the enormous increases in diseases such as obesity and diabetes among the young, it seems important to ask whether disability trends have been different for younger age groups; indeed, the rate of obesity alone has more than doubled for the young over the past two decades.⁴ Other researchers have argued that as a result of changes to public disability insurance programs, the young face growing incentives to report disability, even if their actual level of disability has remained constant.⁵ The young seem to be facing greater disability risk from disease, and more powerful incentives to report disability.

In this paper we use data from the National Health Interview Survey (NHIS) to present a detailed analysis of disability trends in the population ages 18–69. This analysis reveals substantial growth in reported rates of disability in population younger than age fifty but not among the elderly. These trends do not appear to be the result of changes in the composition of the population or of changes in specific survey procedures. In the interest of stimulating further research, we present several different explanations for rising disability levels: obesity, technological advances in medicine, and more generous disability insurance. We briefly outline the evidence that is consistent and inconsistent with each. None fits the data perfectly, but all contain important insights and the seeds for future analysis. Finally, we discuss the possible impact of disability among the young on public programs like Social Security Disability Insurance (SSDI), Medicare, and Medicaid.

Study Methods

Top Editor's Notes Study Methods Study Results Discussion Conclusion Notes

 
We used NHIS data from 1984 to 2000, which contain individual-level information on the demographic and health status of a nationally representative sample of the U.S. civilian, noninstitutionalized population; these data have been collected every year since 1957.⁶ Although the survey was redesigned in 1982 and again in 1997, one can construct consistent estimates of disability from 1984 to 1996. (In 1982 and 1983 the NHIS did not ask the questions we use to measure disability.) Moreover, it is possible to construct a separate, internally consistent series from 1997 to 2000. Unfortunately, comparisons across the two series are not possible, because the survey instrument underwent considerable changes between 1996 and 1997. Nonetheless, from 1982 to 1996 and again from 1997 to 2000 there were no changes to the disability sections of the questionnaire. For all of the available NHIS years, we constructed estimates of disability that account for the complex survey design.⁷

From its inception, the NHIS has asked respondents whether their health limited their ability to work or perform housework. These questions are problematic for the measurement of disability because they are influenced by a person’s decision to stay in the labor force as well as by a person’s choice of occupations. For example, a given physical impairment could represent a work limitation for a bicycle messenger but not for an accountant. The NHIS began asking questions more suited to measuring disability in 1984. All respondents over age five reporting an activity limitation were asked if they needed help with personal care or other routine needs. These questions move toward a more common baseline of normal activity: Bicycle messengers might differ from accountants in the requirements of their jobs, but they probably differ by much less in their personal care requirements.

Based on the answer to the personal care question, each respondent is placed in one of three ordered categories: (1) unable to attend to personal care needs; (2) limited in performing other routine tasks; and (3) not limited in attending to personal care or performing routine tasks. We say that a person has a "routine-needs" disability if he or she is in category 1 or 2 and that a person has a more severe "personal-care" disability if he or she is in category 1. We interpret category 2 to be less severe, and thus less inclusive, than category 1. Since both levels of disability seem to be caused by similar types of illnesses, the difference between them would appear to be one of severity and degree, rather than a fundamental qualitative difference in the kind of disability being measured. For example, by far the most common causes of both kinds of disabilities among people ages 18–39 are musculoskeletal (especially back) problems and mental illness.⁸

Disability data are also available in the 1997–2000 NHIS data sets, albeit with some modifications. Because of several subtle changes in the wording of the disability questions and in survey methodology, it is inappropriate to compare data from before and after the 1997 survey. However, we were still able to use the disability data from this period to group respondents into one of the three categories listed above.

To smooth the disability trends within age categories, we pooled adjacent years of data. From the seventeen years of survey data, we constructed nine periods: 1984, 1985–86, 1987–88, 1989–90, 1991–92, 1993–94, 1995–96, 1997–98, and 1999–2000. We measured the raw change in disability over time, from 1984 to 1996 and from 1997 to 2000, as well as whether or not these raw changes differ statistically from zero.

We used multivariate regression to assess whether or not the aggregate trends are driven by changes in the composition of the population. We adjusted for sex, race, Hispanic origin, employment status, and schooling.⁹ The adjusted numbers report the growth in disability that would have occurred absent changes in the composition of the population by race, sex, Hispanic origin, educational attainment, and employment status.

Study Results

Top Editor's Notes Study Methods Study Results Discussion Conclusion Notes

 
Aggregate trends. Exhibit 1 measures disability as the proportion of the population unable to attend to personal care needs or perform other routine tasks (either category 1 or category 2 above), and alternatively as the more restricted population unable to attend to personal care needs alone (category 1 only). It is worth reemphasizing that the numbers before and after 1997 are not directly comparable, although comparisons can be made within the two periods.

From 1997 to 2000 there were continuing, but modest and primarily insignificant, increases in disability for people under age fifty and insignificant declines for those over age fifty. It is likely that more years of data are required before we can draw firm conclusions about the period beginning in 1997, but a few interesting facts are worth noting. First, growth in the more severe personal-care-limitations measure seems to have occurred for those ages 40–49, who were the only ones under age fifty to escape such increases in the earlier period. Second, the biggest absolute declines in routine-needs disability occurred for those over age fifty. While these trends are not statistically significant, they are consistent with the differences between younger and older populations.

Accounting for compositional change. Although the raw changes in disability are informative, we would like to know whether the changes in disability have been driven simply by changes in the composition of the population. Exhibit 2 presents trends in disability, regression-adjusted for compositional changes in age, sex, race, educational attainment, and employment status. The values from 1984 to 1996 should be interpreted as the rate of disability that would have prevailed if the composition of the population (by the above characteristics) had remained fixed at its 1984 levels. Similarly, the values from 1997 to 2000 represent the rates that would have prevailed if composition had been fixed at its 1997 levels.

Once again, the evidence for 1997–2000 is inconclusive. There are no statistically significant changes over this period, probably because the time frame is too short. If we take the point estimates at face value, however, it appears that growth in disability might be leveling off for the groups under age fifty, which are also the groups that experienced the largest increases from 1984 to 1996.

Discussion

Top Editor's Notes Study Methods Study Results Discussion Conclusion Notes

 
The traditional focus of disability research has been on the elderly, with good reason. Disability is much more prevalent among the elderly, and it has more direct impact on the demand for medical care in this age group. However, the emerging growth in disability among the young merits further attention by researchers and policymakers, because it has an important social and economic impact. It affects the demand for both medical care and publicly provided disability insurance; it also affects disability among tomorrow’s elderly.

Developing and justifying a definitive explanation for the growth in reported disability from 1984 to 1996 is beyond the scope of this paper. However, here we suggest some possible candidates, along with the evidence that is consistent and inconsistent with each. There are at least two types of explanations, which are not mutually exclusive. The growth in disability could be the result of real deterioration in underlying health, or it could be the result of increased incentives to report disability.

Influence of obesity. The recent rise in obesity levels represents one plausible reason why there might have been real deterioration in health. For each age group that we examined, the rate of obesity has increased by at least 700 per 10,0000 from 1984 to 1996, or by seven percentage points. Exhibits 3 and 4 present some relevant data that help to quantify the effect of this trend on disability.

View larger version (15K): [in this window] [in a new window]   EXHIBIT 3 Rate Of Routine-Needs Disability Per 10,000 Population, By Age Group And Obesity Status, 1990

View larger version (12K): [in this window] [in a new window]   EXHIBIT 4 Effect Of Obesity On Disability, By Age Group, 1984–1996

To estimate obesity’s effect on disability, Exhibit 4 accounts for the growing prevalence of obesity combined with higher rates of disability among the obese, and also accounts for the more rapid rate of disability growth among those who are already obese.¹¹ The result is a crude but intriguing estimate of how much obesity could have contributed to disability growth. The contribution varies by age group, but it is clearly the dominant factor for those ages 50–59: Among this age group, disability rose only among the obese. Obesity accounts for about half of the increased disability among those ages 18–29; about one-quarter for those ages 30–39; and about one-tenth for those ages 40–49. Exhibit 4 demonstrates the primary weakness of an explanation emphasizing obesity growth: namely, its prevalence across all age groups, including the elderly. As we emphasize, therefore, a full explanation of disability trends is likely to require many pieces.

A more comprehensive view of the links between various diseases and disability appears in Exhibit 5, which breaks down the primary cause of disability for the population ages 18–59 with a routine-needs disability. The exhibit makes plain the earlier observation that the two most important causes of disability among the nonelderly are musculoskeletal problems and mental illness. It also shows that disability cases from musculoskeletal problems (which are primarily back-related) and diabetes are growing more rapidly than those from other problems. Together, diabetes and musculoskeletal problems accounted for about seven percentage points more cases in 1995–96 than in 1984. Although diabetes accounts for a relatively small proportion of cases, the proportion doubled over this period of time, which suggests that it is becoming an increasingly important source of disability. Whether these problems are attributable to rising obesity is an issue left for further research. Still, the links between diabetes and obesity are well established.¹² There is also some evidence that obesity exacerbates musculoskeletal, especially back, problems.¹³

View larger version (23K): [in this window] [in a new window]   EXHIBIT 5 Composition Of Primary Conditions Causing Routine-Needs Disability Among People Ages 18–59, 1984–1996

Role of disability insurance incentives. The above explanations seek to show why the health of the population might have deteriorated, but it is also possible that trends in disability reflect forces other than health, namely, changes in the economic incentives for disability insurance. As a result of the benefits formula employed, disability insurance has become relatively more attractive to less-skilled workers in recent years. Disability insurance benefits are inflated according to average wage growth, but as a result of expanding wage inequality, less-skilled workers are experiencing below-average wage growth. As a result, their potential disability benefits might be growing faster than their potential market wages. Several researchers have found that this trend could have encouraged less-skilled workers to file for disability insurance more often, even though they might not have become more disabled.¹⁴

Growth in per capita disability claims indeed occurred between 1984 and 1996, as did expansion in the incentives for disability insurance.¹⁵ It is possible that people who are no more disabled are nonetheless more likely to claim disability insurance and thus self-report disability in surveys. Just like the earlier explanations, however, this has weaknesses of its own. As mentioned earlier in our discussion of compositional change, rates of personal-care and routine-needs disability rose uniformly across all education groups and for people both outside and inside the labor force. In contrast, the disability insurance explanation would predict declining disability reports within the labor force, and it would predict that disability growth ought to be more pronounced among less educated groups. It is difficult to find these trends in our data.

Conclusion

Top Editor's Notes Study Methods Study Results Discussion Conclusion Notes

 
Disability is not just a feature of old age. Economic development and technological change in health care have allowed people of all ages to live in frailty with greater ease than at any other time in history. From the mid-1980s to mid-1990s, reported rates of disability have grown among the young, even as the old have become relatively healthier. Moreover, this growth seems to have occurred within all demographic and economic groups, rather than within isolated segments of the population.

Although the source of these trends is not yet clear, it is clear that rising rates of reported disability will have adverse consequences for public programs. Even if increased disability is the result of changing incentives for disability benefits and not the result of actual deterioration in health, the SSDI system is likely to feel the effects. David Autor and Mark Duggan report that the proportion of nonelderly adults receiving SSDI benefits rose from 3.1 percent to 5.3 percent between 1984 and 2000; in absolute terms, the number of nonelderly recipients doubled.¹⁶ These numbers are much larger in magnitude than the number of people with routine-needs or personal-care limitations, presumably because work-limiting disabilities are less severe than those that limit personal care. This suggests that the increase in routine-needs limitation could understate the impact on the SSDI program, which is even affected by less severe forms of disability.

If—as we have argued—at least part of the increase in disability is attributable to deterioration in health among the young, the effects are likely to be felt in the U.S. health care system. Elsewhere, we have explored the future impact of disability among the young on the long-term care industry (and the Medicaid program that funds much of it) and on Medicare. Using forecasts based on data from the NHIS and the Medicare Current Beneficiary Survey (MCBS), we suggest that the recent growth in disability among the young could lead to a future nursing home population that is 10–25 percent larger than it might otherwise have been.¹⁷ Similar forecasting methods suggest that Medicare expenditures could be 10–15 percent higher than they would have been in the absence of this disability expansion.¹⁸ Given the inevitable increase in the level of resources devoted to medical care for an aging population, these percentage increases loom even larger for the future of the nation’s health care system.

Editor's Notes

Top Editor's Notes Study Methods Study Results Discussion Conclusion Notes

 
Darius Lakdawalla is an economist at RAND in Santa Monica, California. Jay Bhattacharya is an assistant professor of medicine at the Center for Primary Care and Outcomes Research, Stanford University School of Medicine, in California. Dana Goldman is director and corporate chair, Health Economics, at RAND.

The authors are grateful for the comments and suggestions of Michael Hurd, Geoffrey Joyce, and Constantijn Panis. This research was funded by the Centers for Medicare and Medicaid Services (Contract no. 500-95-0056) and the National Institute on Aging (Grant no. 5P01AGO8291). The statements and opinions contained in this paper are solely those of the authors, who assume full responsibility for their accuracy and completeness.

Notes

Top Editor's Notes Study Methods Study Results Discussion Conclusion Notes

 

1. E.M. Crimmins, Y. Saito, and D. Ingegneri, "Changes in Life Expectancy and Disability-Free Life Expectancy in the United States," Population and Development Review 15, no. 2 (1989): 235–267.[CrossRef][ISI]
2. E.M. Gruenberg, "The Failures of Success," Milbank Memorial Fund Quarterly 55, no. 1 (1977): 3–24.
3. E.M. Crimmins, Y. Saito, and S. Reynolds, "Further Evidence on Recent Trends in the Prevalence and Incidence of Disability among Older Americans from Two Sources: The LSOA and the NHIS," Journals of Gerontology Series B: Psychological Sciences and Social Sciences 52B, no. 2 (1997): S59–S71; K.G. Manton, L. Corder, and E. Stallard, "Chronic Disability Trends in Elderly United States Populations: 1982–1994," Proceedings of the National Academy of Sciences (U.S.) 94, no. 6 (1997): 2593–2598; and R.F. Schoeni, V.A. Freedman, and R.B. Wallace, "Persistent, Consistent, Widespread, and Robust? Another Look at Recent Trends in Old-Age Disability," Journals of Gerontology:SeriesB,Psychological Sciences (July 2001): S206–S218.
4. A.H. Mokdad, et al., "Diabetes Trends in the U.S.: 1990–1998," Diabetes Care 23, no. 9 (2000): 1278–1283[Abstract/Free Full Text]; and A.H. Mokdad et al., "The Continuing Epidemic of Obesity in the United States." Journal of the American Medical Association 284, no. 13 (2000): 1650–1651.[Free Full Text]
5. W.J. Nelson Jr., "Disability Trends in the United States: A National and Regional Perspective," Social Security Bulletin 57, no. 3 (1994): 27–41; J. Bound and T. Waidmann, "Accounting for Recent Declines in Employment Rates among the Working-Aged Disabled," NBER Working Paper no. 7975 (Cambridge, Mass.: National Bureau of Economic Research, 2001); andD.H. Autorand M.G. Duggan, "The Rise in the Disability Rolls and the Decline in Unemployment," Quarterly Journal of Economics 118, no. 1 (2003): 157–205.[CrossRef][ISI]
6. The exclusion of the institutionalized appears to have little effect on our results, as discussed in an appendix available at www.rand.org/publications/TR/TR104.
7. Ibid., for more detail on our estimation procedures.
8. Personal-care limitation tends to be caused by mental retardation and disorders of the back; these accounted for one-third of personal-care disability cases among those ages 18–39 in 1995. Similarly, routine-needs limitations tend to be caused by these two conditions, as well as the two related conditions of rheumatism and personality disorder.
9. The details of the adjustment procedure are spelled out more fully at www.rand.org/publications/TR/TR104.
10. Manton et al et al., "Chronic Disability Trends"; K.G. Manton and X. Gu, "Changes in the Prevalence of Chronic Disability in the United States Black and Nonblack Population above Age Sixty-five from 1982 to 1999," Proceedings of the National Academy of Sciences (U.S.) 98, no. 11 (2001): 6354–6359.
11. The details of this calculation are available at www.rand.org/publications/TR/TR104.
12. Mokdad et al., "Diabetes Trends in the U.S."
13. M. Peltonen et al., "Musculoskeletal Pain in the Obese: A Comparison with a General Population and Long-Term Changes after Conventional and Surgical Obesity Treatment," Pain 104, no. 3 (2003): 549–557.[CrossRef][ISI][Medline]
14. Bound and Waidmann, "Accounting for Recent Declines"; and Autor and Duggan, "The Rise in the Disability Rolls."
15. Autor and Duggan, "The Rise in the Disability Rolls."
16. Ibid.
17. D. Lakdawalla et al., "Forecasting the Nursing Home Population," Medical Care 41, no. 1 (2003): 8–20.[Medline]
18. D. Goldman et al., "Disability Trends and Future Medicare Costs," in Frontiers in Health Policy Research, vol. 7, ed. D. Cutler and A. Garber (Cambridge, Mass.: MIT Press, forthcoming).

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