Demography Of Disability Research Paper

1994). It has gained in popularity as a framework for thinking about the needs of the world’s aging population. More recently, this framework has been applied to understand disability among children, persons entering the labor force, and working-age adults, with an emphasis on supportive services, such as home health and physical therapy, to improve or maintain physical functioning and other aspects of quality of life, and elimination of environmental barriers.

1. History Of Disability Measurement

1.1 Work Limitation

Traditionally, demographers relied on census data on the number and characteristics of people, combined with information on death from vital statistical systems, to project the working age population. A table of working life added age-specific data on labor force participation (Wolfbein 1949). This system proved unworkable, as many persons of working age are limited in their labor force participation and others retire voluntarily. While these causes of being out of the labor force could be handled with multiple decrement life tables, the recognition that people in these situations often re-entered the work force reduced the value of this working life table approach (Schoen and Woodrow 1980).

Despite these practical problems, nations found it essential to be able to project the numbers of workers by age, sex, and educational levels, the numbers of these workers who will be employed under current and alternative projections of the demand for workers, the number of working-age persons who are disabled or limited in labor force participation, and the retired population who would draw on pension systems. This necessitated an individual level of analysis in which more direct data on factors in labor force participation (including health and disability) can be collected, and the use of methods for event history data to identify the demographic social variables involved.

To estimate the scope of disability within countries, scientists have devoted substantial effort to the development of valid measures. Health interview surveys in Europe and the USA collected data on disability in large populations as early as the late 1800s and the early 1900s. Disability was measured as the prevalence of days of sickness per 1,000 persons and the number of people who were sick and unable to work on the day of interview, thus introducing a measurement approach still in use in current large-scale surveys. In addition, measures of labor force participation were expanded to include persons who report they are not working because of disability.

1.2 Activities Of Daily Living

In 1949, the Commission on Chronic Illness was established in recognition of the high prevalence of chronic illness in the USA. The Commission called for a classification of difficulty in the performance of activities of daily living in order to measure the disabling impact of chronic illnesses and conditions on people’s lives. A number of scales of this type emerged in the 1950s. Among the most valid and replicable is the Index of Activities of Daily Living (ADLs), constructed on the basis of empirical observations of patients’ recovery of ability to perform necessary daily tasks after hip fracture (Katz et al. 1963). Standard ADLs include bathing, dressing, toileting, transferring in and out of bed and chairs, eating, and getting around inside the house. Measures more indicative of cognitive than physical impairment, e.g., using the telephone and managing medications, are often included also. This scale and its many hybrids have been in use since it was developed, both to monitor the decline and recovery processes in individuals, and also to measure levels of disability in populations.

Given that ADL scales tap levels of disability most relevant to the very frail, Lawton and Brody (1969) devised the Instrumental Activities of Daily Living (IADL) Scale, designed to measure competence at a more complex level than the basic ADL scale. This scale includes activities more typically problematic for people with chronic conditions who live in the community, such as shopping, housework, and the ability to handle finances. Unlike ADLs, which are mainly applicable to people in long-term care institutions, IADLs are particularly useful in capturing variation in physical functioning among community-dwelling populations. Severity of disability at the population level is typically measured by counts of activity limitations, e.g., the proportion of the population with one or two ADL limitations versus three or more. While in general limitations in ADLs are indicative of a more severe disability than IADLs, empirical research has not identified a strict hierarchical order. Nevertheless, estimates of disability are often framed in terms of the proportion of the population with (any) ADL limitations, and separately, with (any) IADL limitations. More recently, it has become common to ask survey respondents who indicate difficulty in activity performance whether they need help, and whether needed help is received; thus generating estimates of unmet need for services.

In specialized studies of disability during the 1990s these scales have been supplemented by questions that tap a variety of physical impairments, including a series of questions developed by Saad Nagi to measure mobility and flexibility, e.g., ability to walk a quarter mile (Nagi 1979). Such studies generally include measures of sensory impairments as well, including the ability to see, hear, and communicate. The strategy to use measures of daily activity, ability to perform basic tasks, and participation in age and gender-appropriate roles and functional capacities is widely applicable over the life span, in developed nations, and among different socioeconomic and cultural groups. Such measures provide an indication of level of need for medical and supportive services and equipment within given populations. For persons not covered by old age medical insurance plans, information on access to and cost coverage for services for potentially disabling health conditions is essential. In the USA both cost restrictions and lack of access to appropriate services are factors sometimes preventing appropriate medical care and support services for both children and adults.

2. Considerations And Cautions In Disability Measurement

While still in widespread use, the applicability of measurement of limitation in major activities (i.e., work, housekeeping, and going to school) is limited and interpretation is difficult. Limitation in ability to work is very much determined by what one does for a living, for example. Two people with similar health profiles may report limitation in major activity quite differently if one is a construction worker and the other a teacher. Furthermore, it is often difficult to define one’s major activity, particularly for people of retirement age. Thus, while this measure may be helpful in estimating attrition from the work force due to disabling health conditions, it is not a precise measure of the prevalence or severity of disability in populations. Limitation in ‘any’ or ‘other’ activities presents even greater challenges to interpretation.

Use of measurement of limitations in ADLs IADLs has far wider application as a measure of disability in populations, although such measures do have problems too. Differences in question wording, the specific activities included in measurement, and differences in study design can result in variation in estimates of ADL variation across surveys of community dwelling populations.

While ADLs such as bathing and dressing have universal meaning, IADLs such as shopping and cooking have a strong gender role component, which can result in substantial underestimates of disability for men. Thus, ADL measures are more ‘pure’ measures of physical function than IADLs, while assessment of IADL disability has a greater subjective component.

Other confounding influences in measurement of ability to perform daily living activities include the measurement of capability (‘Can you …’) versus actual performance (‘Do you …’), ascertainment of difficulty (‘Do you have difficulty with …’) versus dependency (‘Do you receive help with …’), inclusion versus exclusion of human help and/or special equipment in ascertaining difficulty (‘Even with help and/or use of special equipment, do you have difficulty …’), and use of proxy vs. self-reporting. The necessarily subjective nature of disability measurement presents challenges for researchers to achieve comparability across studies within countries. Nuances in languages present even greater challenges to assessing the scope of disability across nations.

3. Demographic Methods For The Study Of Disability

The recognition that disability is a phenomenon best measured at the individual level has led to great advances in the demographic study of disability. Crucial to this new approach is the recognition of disability as a dynamic process characterized by entries and exits and competing risks. Thus studies of labor force participation among older workers have been designed to take into account potentially disabling medical conditions, type of job and work disability, shift to alternative jobs where the condition is not disabling, and the competing state of retirement, as well as movements into and out of these statuses. Both multidimensional life tables and methods for event history analysis have proved useful (Manton et al. 1992). The use of event history methods has proved to be of particular value because of their ability to incorporate demographic or socioeconomic covariates that affect these processes. The greatest advances have come in the study of the elderly, but these methodologies should prove powerful in the study of disability among children, the transition from adolescence to adulthood, and the situations of adults who have not reached old age. A shortcoming of this research approach as currently practiced is that it tends to focus exclusively on the individual instead of an individual within an environment that may present obstacles or provide assistance, though extension to include contextual variables is possible.

4. Current Trends In Disability

4.1 Activity And Work Limitations

Worldwide concerns about population aging and the likely increase in rates of disability associated with lengthening life expectancies have escalated research interest in the measurement of population disability trends. In the USA, a variety of cross-sectional and longitudinal national surveys are available to determine current disability rates as well as disability trends over the past several decades. Overall, annual estimates of disability (measured as activity and work limitations) available from the National Health Interview Survey since 1970 indicate that the proportion of the US population with disabilities has increased during that time period.

When disability rates are calculated by age group, it is clear that the elderly experience disability at approximately twice the rate of people between ages 45 and 64, and at four times the rate of the younger working age group (aged 18–44). Thus, the increase in the proportion of the population who are elderly contributes to the increase in rates of disability in the larger population, although actual rates of activity limitations among persons 65 and older remained relatively constant from the early 1980s to 1994, estimated at about 38 percent for men, and 39 percent for women (Kaye et al. 1996).

Activity limitation rates have also remained constant among the older working age group (ages 45–64) since the early 1980s, at about 22 percent for men, and 23 percent for women. Work disability is relatively constant in this population, with 11 percent unable to work and 7 percent limited in amount and/or kind of work. In contrast, disability has increased somewhat among people under 45 years of age, particularly in the early 1990s. From 1990 to 1994, activity limitations among younger men (aged 18–44) increased from 8.7 percent to 10.2 percent, and among younger women from 8.9 percent to 10.3 percent. During the same time period, the proportion of this subgroup that is unable to work increased from 2.9 percent to 3.7 percent.

Similarly, activity limitations among children have increased in the early 1990s, from 5.6 percent to 7.9 percent among boys, and from 4.2 percent to 5.6 percent among girls. These increases are reflected in an increase in the prevalence of asthma and cognitive disorders such as Attention Deficit Disorder and learning disabilities. Thus, increases in disability among younger adults and children, combined with an increase in the proportion of the population who is elderly, are largely responsible for the trend toward higher disability levels in the overall US population (Kaye et al. 1996).

4.2 ADL/IADL Disability Trends

There is a growing consensus that while rates of certain chronic diseases have increased in recent decades, both in the USA and in other countries, rates of disability in daily living activities have actually decreased within the elderly population. Early reports of this decrease were met with skepticism, with some researchers attributing apparent decline to an artifact of question wording or survey design. However, increasing consistency in findings across several longitudinal US surveys provide reliable evidence that disability, has decreased from the early 1980s until the early 1990s particularly in IADLs (Manton et al. 1998). Findings regarding improvement in ADL disability are less consistent.

Researchers have begun to focus their work on identifying factors that account for observed decline. Advances in medical technology and disease management as well as improved access to medical and support services and technical aids that may reduce difficulty in task performance have been credited with at least some of the reduction in measured disability levels. However, recent evidence suggests that education is the most important factor associated with disability decline in the US population, as a less educated cohort of elderly persons is being replaced by a cohort of people raised in more prosperous times. Attribution of disability decline to increases in educational levels suggests that observed decline may continue, albeit at a reduced rate (Freedman and Martin 1999).

The Global Burden of Disease Project has undertaken the massive task of estimating the incidence and prevalence of disability for world regions, for men and women across the lifespan (Murray and Lopez 1996). In this work the expectation of life at birth is divided into years of life without disability and with disability. In the established market economies males can expect a life at birth of 73.4 years, of which 8.1 percent will be spent in disability. Women’s expectation of life at birth is 80.5 years, of which 8.3 percent will be spent in disability. While women spend more time than men in the disabled state because of their longer life span, that longer life span itself does not lead to an inevitable increase in the percentage of years in disability. Indeed, in those regions with an expectation of life at birth of less than 60 years, more person years are spent in disability than in nations with lower mortality, with 12 percent or higher of the lifespan lost due to disability. Similar observations apply to calculations for the population at age 60 as well. The best strategy for relieving disability over the lifespan is to begin promoting health among younger adults in order to reduce disability in later middle age and old age.

Bibliography:

1. Freedman V A, Martin L G 1999 The role of education in explaining and forecasting trends in functional limitations among older Americans. Demography 36: 461–73
2. Katz S, Ford A B, Moskowitz R W, Jackson B A, Jaffe M W 1963 Studies of illness in the aged: The index of ADL. Journal of the American Medical Association 185: 914–19
3. Kaye H S, LaPlante M P, Carlson D, Wenger B L 1996 Trends in disability rates in the United States, 1970–94. In: Disability Statistics Abstracts 17. Disability Statistics Center, University of California, CA
4. Lawton M P, Brody E M 1969 Assessment of older people: Self-maintaining and instrumental activities of daily living. The Gerontologist 9: 179–86
5. Lawton M, Powell B E 1969 Assessment of older people: Self-maintaining and instrumental activities of daily living. Gerontologist 9: 179–88
6. Manton K G, Woodbury M A, Stallard E, Corder L S 1992 The use of grade of membership techniques to estimate regression relationships. Sociological Methodology 2: 321–81
7. Manton K G, Stallard E, Corder L S 1998 The dynamics of agerelated disability 1982–1994 in the US elderly population. Journal of Gerontology, Biological Sciences 53A: B59–B70
8. Murray, C J L, Lopez A D 1996 Global and regional descriptive epidemiology of disability: Incidence, prevalence, health expectancies and years lived with disability. In: Murray C J L, Lopez A D (eds.) The Global Burden of Disease: A Comprehensive Assessment of Mortality and Disability from Diseases, Injuries, and Risk Factors in 1990 and Projected to 2020. Harvard University Press, Boston, pp. 201–46
9. Nagi S Z 1979 The concept and measurement of disability. In: Berkowitz E D (ed.) Disability Policies and Government Programs. Praeger, New York
10. Schoen R, Woodrow K 1980 Labor force status life tables for the United States 1972. Demography 17: 297–322
11. Verbrugge L M, Jette A M 1994 The disablement process. Social Science in Medicine 38: 1–14
12. Wolfbein S L 1949 The length of working life. Population Studies 3: 286–94