d i s a b i l i t y a n d r e h a b i l i t a t i o n , 1999 ; v o l . 21, n o . 8, 388± 391

Implications of alternative de® nitions ofdisability beyond health care expenditures

DIDI M. W. KRIEGSMAN ‹ Œ * and DORLY J. H. DEEG �

‹ Institute for Research in Extramural Medicine

ΠDepartment of General Practice, Nursing Home Medicine and Social Medicine, EMGO Institute, Van

der Boechorststraat 7, 1081 BT Amsterdam, The Netherlands

� Department of Psychiatry and Department of Sociology and Social Gerontology, Vrije Universiteit,

Amsterdam, The Netherlands

Introduction

The paper of Tepper et al." deals with the relationship

between alternative de® nitions of disability and in-

dividual health expenditures. Unfortunately, the main

issue, namely that alternative de® nitionsof a determinant

may in¯ uence the magnitude of the outcomes, is

obscured by the fact that the paper lacks a clear focus:

the message is obscured by the broader issues referred to

in both the introduction and the discussion sections,

which are not substantiated by the data. In addition,

there appear to be several methodological shortcomings

in the paper that are not addressed properly. As a result,

we feel that the importance of the results presented is

generalized far beyond what the study and the data

allow. In this commentary, we will ® rst discuss the paper

of Tepper et al." and, thereafter, provide a more

generalized view on the policy relevance of alternative

de® nitions of determinants in relation to health-care

expenditures.

Appropriateness of the assumptions

The analyses are justi® ed by assumptions that are

subject to debate. It is assumed that individual health

care expenditures are of primary importance in guiding

federal policy. The importance of individual health

expenditures for policy is overestimated. There is hardly

any direct relationship between individual health ex-

penditures and total health care costs : individual

expenditures may show large variations in the course of

time; whereas total health care costs are unaŒected by

these variations. For policy, total health care costs, either

absolutely or as a percentage of the gross national

product, are far more important. On the level of absolute

* Author for correspondence.

amounts spent on health care, more money is spent for

the large percentage of people with less severe disability,

than for the small percentage with severe disability, in

spite of the fact that, as presented in the paper by Tepper

et al.," the latter group has a more than three-fold higher

individual health expenditure. It can be assumed that,

particularly in those with less severe levels of disability,

there are possibilities of improvement or even recovery.

Thus, in the long run, the implementation of successful

programmes directed at improving functioning of people

with less severe levels of disability will have a far more

pronounced eŒect on health care costs than those

directed at the small fraction of people with severe

disability. The authors also state that disability-related

expenditures are particularly important for policy plan-

ning. However, a large proportion of the total health

care expenditure arises from causes that are not

necessarily related to long term disability; injuries and

chronic diseases in the working age population and

chronic diseases in the elderly population.# Disability is

indeed caused mainly by chronic diseases, both in the

working age and in the elderly population. A higher

number of chronic diseases is consistently associated

with a higher prevalence of disability,$ ± & and longitu-

dinally with a higher incidence of disability.’ However,

there are marked diŒerences between the strengths of the

associations with disability across diŒerent chronic

diseases, largely depending on the clinical characteristics

of these diseases. In addition to diŒerences between

diseases, we have previously shown that there are also

considerable diŒerences within disease categories, which

are related to the severity of the disease involved.( , )

Health care utilization, and thereby also health expen-

ditures, are diŒerently associated with disability, de-

pending on the chronic disease involved: cancer and

hypertension were shown to have little eŒect on

disability, while having a direct eŒect on utilization;

Disability and Rehabilitatio n ISSN 0963-828 8 print} ISSN 1464-516 5 online ’ 1999 Taylor & Francis Ltdhttp:} } www.tandf.co.uk } JNLS } ids.htm

http:} } www.taylorandfrancis.com } JNLS } ids.htm

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Alternative de® nitions of disability

other common chronic diseases, such as cardiac disease

and diabetes mellitus exert both an indirect in¯ uence on

utilization through disability and a direct eŒect on

utilization. *

The authors assume that the lack of speci® cation in the

de® nition of disability is particularly consequential in the

working age population. However, in this age group,

apart from chronic diseases, injuries are the leading

cause of disability.# Because of this and because of the

lack of a speci® cation with regard to duration of

disability in the paper by Tepper et al.," it is doubtful

whether their statement is true. It may be possible that a

large proportion of disability in the study population is,

in fact, short-term disability related to injuries. The

argument that is provided, namely that the working age

population is more heterogeneous than, for instance, the

elderly population, is also not substantiated by refer-

ences. In the elderly population levels of disability vary

as widely as in the working age population, ranging from

no disability at all to chronically bedridden. The only

diŒerence is that the prevalence of disability (regardless

of which de® nition is used) may be higher in the elderly

population. Thus, the elderly population is as hetero-

geneous as the working age population with regard to

levels of disability. In addition, the indirect costs of

disability that are of particular importance in the

working age population, such as the costs of lost

productivity and disability pensions, are not mentioned

at all. The importance of these indirect costs is illustrated

by the fact that in non-insulin-dependent diabetes

mellitus, which is associated with severe disability in

16.5% of the patients (which is lower than for many

other chronic diseases), the indirect costs (excluding

those due to premature mortality) were almost 20 % of

the total economic costs of the disease in 1986, the

proportion being even higher in the working age

population. " !

Methodological Considerations

The authors do not discuss the implications of the

non-representativeness of the NMES sample. Popula-

tions known to be at a greater risk of needing services to

treat chronic conditions or long-term illness were

oversampled. It is clear that this sampling frame also

results in overrepresentation of subjects with disability,

as well as increasing the measured health care expendi-

tures above that of the general population. Unfortu-

nately, these sources of bias are not taken into account in

the analyses, nor are the possible implications for the

generalizability of the results discussed. In contrast to

several other published papers based on NMES data,# , " "

which give ® gures extrapolated to provide information

on the general population in the US, the ® gures presented

by Tepper et al. " are based on a straight forward analysis

of the information obtained from the study sample of

19737 individuals. Given the non-representativeness of

this sample, the prevalences of disability are biased

upwards. Although this does not necessarily imply that

the estimates of individual health expenditures are also

biased, the oversampling of speci® c groups at greater risk

of needing services does. Another methodological issue

concerns the fact that the NMES sample is based on

households; the mean number of persons per household

included in the NMES is 2.5 (35000 individuals in 14000

households). One might question the possibility of

disentangling individual health care expenditures from

household health care expenditures. Unfortunately, there

is insu� cient information provided on the method of

data acquisition, that is, how were individual health care

expenditures assessed within the household sampling

frame, to make sure that the ® gures for individual

expenditures are su� ciently reliable. Also, no infor-

mation is provided about the number of households

from which the study sample of 19 737 originates.

Because of the working age of this sample, and the

likelihood there is a comparatively large proportion of

households consisting of parent(s) with children, the

mean household size is probably even larger than 2.5. A

second problem related to the household sampling frame

of the NMES is that working age subjects living in an

institution are excluded." # Because the health expendi-

tures for this group are higher than those for non-

institutionalized subjects, even when they would have the

same level of disability, individual health expenditures

according to disability level are underestimated. More-

over, there may be regional diŒerences in the chances

that severely disabled persons are institutionalized, for

example because of diŒerent availability of these types of

facilities or diŒerent admission policies. This is another

possible source of bias that is not taken into account.

Regarding the de® nitions of disability, it remains totally

unclear whether they apply to disability `in general ’ (that

is, regardless of the duration) or to chronic disability. It

is common however, that in addition to health-related-

ness, duration of disability is de® ned explicitly as part

of the de® nition." $ This lack of information, which

applies to all the ® ve de® nitions used in the paper

severely limits the interpretation of the results. The ® ve

de® nitions may be applicable for both acute and chronic

disabilities,although the most `severe ’ de® nition includes

a lower limit of 31 days. In addition, some would argue

whether the two least severe de® nitions (`limited in

vigorous or moderate physical activity’ and `limited in

389

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D. M. W. Kriegsman and D. J. H. Deeg

modest physical activity’) should be considered as

disability or rather as functional limitations." % According

to the Nagi scheme, these types of limitations belong to

the latter category." & The distinction between short-term

(acute) and long-term (chronic) disability is, however,

more important than the question of whether the

de® nitions used by Tepper should be labelled as

`disability’ . Tepper et al. paper is an example of the

secondary analysis of data that has been collected

primarily for other purposes, which carries certain risks

(for example, that the research question is suited to the

available data, and that too little attention is paid to the

adequacy of the study population and the data to answer

the research question) that have to be, at least,

acknowledged. " ’ , " ( The authors, however, do not address

the limitations that are associated with this secondary

analysis, nor the limitations that are associated with the

sample selection and with the use of only a selected

population within that sample.

Looking beyond disability and health care expenditures

Although we recognize the importance of distin-

guishing diŒerent levels of disability, both for research

and policy planning, we adhere to the view that it is even

more important to look at the causes of disability, as well

as at health expenditures generated by non-disabling

chronic diseases. With regard to the latter, it should be

kept in mind that, according to 1987 NHIS estimates,

only 35 % of all persons with chronic conditions report

any form of activity limitation." " In 1987, chronic

conditions which were present in 46 % of the total non-

institutionalized population, accounted for 76% of the

direct medical costs in the US." " The three-fold increase

in health expenditures from the least to the most severe

de® nition of disability as reported by Tepper et al." is

impressive, but the proportional increase associated with

chronic diseases, and particularly with comorbidity, is

even larger. On a population level, the health care

expenditure per capita for people reporting two or more

disabling chronic conditions was ® ve times that of those

with no limiting conditions." ) In our view, neither

researchers nor policy makers are likely to bene® t from

`a standard or benchmark de® nition of disability’ ." On

the contrary, in order to be able to estimate health

expenditures over time more accurately, and to measure

programme and policy impacts, more detailed assess-

ments are necessary. Apart from distinguishing between

diŒerent levels of disability, the causes of disability

should be taken into account.

Currently, predictions regarding disability and health

care costs on a population level are mostly computed

using trends in the prevalences of chronic diseases and

disability. It has been shown that the con¯ icting evidence

with regard to future developments of disability free life

expectancy, as far as `compression ’ or `expansion’ of

morbidity is concerned," $ , " * ± # % may be related to the use

of diŒerent de® nitions of disability. It can be assumed

that the most important future changes in population

disability are associated with changes in severity distri-

butions, involving increasing heterogeneity of disability

severity but with, on average, a shift toward milder

levels. " $ , # ! With regard to the causes of disability,

measures to prevent the onset of fatal diseases, such as

cancer, may be associated with increases in disability,

and thus, with `expansion of morbidity’ , whereas pre-

vention of diseases associated with disability rather than

mortality may result in `compression of morbidity’ .# &

Contrary to how it is usually treated in research and

policy planning, disability is not necessarily a steady

state, but a dynamic process." % , # ’ Disability is the result

of the interaction between environmental and social

demands on the one hand, and the individual’ s capacities

to satisfy those demands on the other hand." % , # ( , # )

Although ageing is generally associated with increasing

prevalences of chronic diseases and disability, substantial

proportions of improvement in disability have been

reported, even in the very elderly.# ’ , # * Also, adequate use

of equipment and personal assistance, instead of being

just an indicator of disability and associated dependency

in physical functioning, were shown to be very e� cacious

in reducing disability.$ ! Although injuries are another

important cause of disability,particularly in the working-

age population, the proportion of disability attributable

to chronic diseases far exceeds that attributable to

injuries. The importance of chronic diseases as deter-

minants of both disability and health care costs will

further increase during the coming decades, primarily

because of the rapid growth of the oldest age groups.$ " In

conclusion, both research and policy planning will bene® t

from more detailed studies on disability. These studies

should ideally encompass information on all ages and

also include the institutionalized proportion of the

population. In addition, accurate measures of the most

important causes of disability should be included, namely

chronic diseases and injuries, as well as parameters of

clinical severity. Disability should be measured in such a

way that diŒerent levels of severity can be distinguished

and the use of equipment or personal assistance to

reduce disability should be taken into account. This type

of detailed information about determinants of health

care costs, causes of disability, severity distributions of

disability and the e� cacy of measures to counter

disability can be of enormous value for policy planning.

390

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Alternative de® nitions of disability

Ideally, such information would enable more detailed

planning, which takes into account longitudinal changes,

such as shifts in the distribution of the clinical severity of

chronic conditions (which can be expected in the coming

decades because of, for instance, earlier detection and

further improvements in medical treatment) and asso-

ciated changes in the severity distribution of disability

and its consequences for health care costs.

References

1 Tepper S, Sutton J, Beatty P, DeJong G. Alternative de® nitions ofdisability: relationship to health-care expenditure. Disability andRehabilitation 1997 ; 19 : 556± 558.

2 Harlan LC, Harlan WR, Parsons PE. The economic impact ofinjuries: a major source of medical costs. American Journal ofPublic Health 1990 ; 80 : 453± 459.

3 Cornoni-Huntley JC, Foley DJ, Guralnik JM. Co-morbidityanalysis : a strategy for understanding mortality, disability and useof health care facility of older people. International Journal ofEpidemiology 1991 ; 20(Suppl. 1) : S8± S17.

4 Verbrugge LM, Lepkowski JM, Imanaka Y. Comorbidity and itsimpact on disability. Milbank Quarterly 1989 ; 67 : 450± 484.

5 Guralnik JM, LaCroix AZ, Everett DF. Comorbidity of chronicconditions and disability among older persons ± United States,1984. Journal of the American Medical Association 1990 ; 263 :209± 210.

6 Guralnik JM, LaCroix AZ, Abbott RD, et al. Maintaining mobilityin late life. I. Demographic characteristics and chronic conditions.American Journal of Epidemiology 1993 ; 137 : 845± 857.

7 Kriegsman DMW. Chronic diseases, family features, and physicalfunctioning in elderly people [Dissertation]. Amsterdam: ThesisPublishers, 1995.

8 Kriegsman DMW, Deeg DJH, Eijk JThM van, Penninx BWJH,Boeke AJP. Do disease-speci® c characteristics add to the ex-planation of mobility limitations in patients with diŒerent chronicdiseases? A study in the Netherlands. Journal of Epidemiology andCommunity Health 1997 ; 51 : 676± 685.

9 Blaum CS, Liang J, Liu X. The relationship of chronic diseases andhealth status to the health services utilization of older Americans.Journal of the American Geriatric Society 1994 ; 42 : 1087± 1093.

10 Huse DM, Oster G, Killen AR, Lacey MJ, Colditz GA. Theeconomic costs of non-insulin-dependent diabetes mellitus. Journalof the American Medical Association 1989 ; 262 : 2708± 2713.

11 HoŒman C, Rice D, Sung HY. Persons with chronic conditions:their prevalence and costs. Journal of the American MedicalAssociation 1996 ; 276 : 1473± 1479.

12 Schoenman JA. Description of the US working age disabledpopulations living in institutions and in the community. Disabilityand Rehabilitation 1995 ; 17 : 231± 238.

13 Verbrugge LM. The experience and measure of disability. In :Mathers C, McCallum J, Robine J-M (eds). Advances in healthexpectancies: proceedings of the 7th meeting of the InternationalNetwork on Health Expectancy (REVES), Canberra, February 1994.Canberra : Australian Institute of Health and Welfare, 1994; 19± 33.

14 Verbrugge LM, Jette AM. The disablement process. Social Scienceand Medicine 1994 ; 38 : 1± 14.

15 Pope AM, Tarlov AR (eds). Disability in America: toward anational agenda for prevention. Division of Health Promotion andDisease Prevention, Institute of Medicine, Washington, DC:National Academic Press, 1991.

16 Kasl SV. Strategies in research on health and aging: lookingbeyond secondary data analysis. Journals of Gerontology 1995 ;50B : S191± S193.

17 Kasl SV. Current research in the epidemiology and public health ofaging: the need for more diverse strategies. American Journal ofPublic Health 1997 ; 87 : 333± 334.

18 Rice DP, LaPlante MP. Medical expenditures for disability anddisabling comorbidity. American Journal of Public Health 1992 ; 82 :739± 741.

19 Olshansky SJ, Ault AB. The fourth stage of the epidemiologictransition: the age of delayed degenerative diseases. MilbankQuarterly 1986 ; 64 : 355± 391.

20 Verbrugge LM. Recent, present and future health of Americanadults. Annual Review of Public Health 1989 ; 10 : 333± 361.

21 Manton KG, Corder LS, Stallard E. Estimates of change in chronicdisability and institutional incidence and prevalence rates in the USelderly population from the 1982, 1984, and 1989 national longterm care survey. Journals of Gerontology 1993 ; 48 : S153± S166.

22 Manton KG, Stallard E, Corder L. Changes in morbidity andchronic disability in the U.S. elderly population: evidence from the1982, 1984, and 1989 national long term care surveys. Journals ofGerontology 1995 ; 50B : S194± S204.

23 Roos NP, Havens B, Black C. Living longer but doing worse :assessing health status in elderly persons at two points in time inManitoba, Canada, 1971 and 1983. Social Science and Medicine1993 ; 36 : 273± 282.

24 Corder LS. Improving survey measurement : health status transi-tions in a longitudinal list sample design. In : Mathers C, McCallumJ, Robine J-M (eds). Advances in health expectancies: proceedings ofthe 7th meeting of the International Network on Health Expectancy(REVES), Canberra, February 1994. Canberra: Australian Instituteof Health and Welfare, 1994; 408± 23.

25 Nusselder WJ, Velden J van der, Lenior ME, Sonsbeek JLA van,Bos GAM van den. The elimination of selected chronic diseases ina population: the compression and expansion of morbidity.American Journal of Public Health 1996 ; 86 : 187± 194.

26 He! bert R, Brayne C, Spiegelhalter D. Incidence of functionaldecline and improvement in a community-dwelling very elderlypopulation. American Journal of Epidemiology 1997 ; 145 : 935± 944.

27 Satariano WA. The disabilities of aging: looking to the physicalenvironment. American Journal of Public Health 1997 ; 87 : 331± 332.

28 Marks D. Models of disability. Disability and Rehabilitation 1997 ;19 : 85± 91.

29 Crimmins EM, Saito Y. Getting better and getting worse :transitions in functional status among older Americans. Journal ofAging and Health 1993 ; 3 : 3± 36.

30 Verbrugge LM, Rennert C, Madans JH. The great e� cacy ofpersonal and equipment assistance in reducing disability. AmericanJournal of Public Health 1997 ; 87 : 384± 392.

31 Schneider EL, Guralnik JM. The aging of America: impact onhealth care costs. Journal of the American Medical Association 1990 ;263 : 2335± 2340.

391

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