Number 170. Mav 26, 1989 

Adva”nce


Data 

From Vital and Health Statistics of the National Center for Health Statistics 

Aging in the Eighties: The Prevalence of Comorbidity 

and Its Association With Disability 

Jack M. Guralnik, M. D., Ph. D., Andrea Z. LaCroix, Ph. D., Donald F. Everett, M. S., National 

Institute on Aging, and Mary Grace Kovar, Dr.P.H., Office of Vital and Health Statistics Systems, 

National Center for Health Statistics 

Introduction 

It is frequently stated that 

the coexistence of multiple 

chronic conditions, referred to 

here as comorbidity, is common 

in the older population. It is 

also assumed that comorbidity 

puts a special burden on older 

people that affects their overall 

health status and fi.mctional 

disability. Although these 

perceptions are supported by 

the experiences of those 

providing care to older patients, 

there has been little work to 

systematically evaluate the 

prevalence, specific patterns, 

and impact of comorbidity in 

community-dwelling representative older populations. 

The prevalence of comorbidity at the time of death has 

been documented using 

multiple cause-of-death data 

from U.S. mortality statistics. In 

1979, more than one cause of 

death was noted on 73 percent 

of all death certificates, with 

33 percent of deaths attributed 

to two causes, 25 percent to 

three causes, and 16 percent to 

four causes or more (l). 

Multiple cause-of-death data 

have also been produced for 

other years and show an 

increase during this century in 

the proportion of deaths 

attributable to more than one 

cause. More than one cause of 

death was reported in 35 

percent of deaths in 1917, with 

this percent rising to 60 percent 

in 1955 and 73 percent in 

1979 (l). This increase is likely 

due to an increase in the 

average age at death, to fewer 

‘Israel RA, Rosenberg HM, Curtin 

LR. Analytic potential for multiple 

cause-of-death data. Am J Epidemiol 

124:161-79.1986. 

deaths resulting from acute, 

infectious diseases, and to more 

complete diagnosis and 

reporting of causes of death. 

Using National Health 

Interview Survey (NHIS) data, 

Rice and LaPlante (2) evaluated the occurrence of multiple 

chronic conditions responsible 

for people’s being limited in 

activity. There were about 1.4 

chronic conditions reported in 

1969–71 and about 1.6 conditions reported in 1979–81 for 

each person 65 years of age and 

older who was limited in 

activity. The average was higher 

than for those under age 65, but 

2Rice DP, LaPlante MP. Chronic illness, disability, and increasing longevity. In Sullivan S, Lewin ME, eds. 

The economics and ethics of longterm care and disability. Washington: 

American Enterprise Institute for 

Public Policy Research, 1988. 

pp. 9-55. 

US, DEPARTMENT OF HEALTH AND HUMANSERVICES National Center for Health Statistics 

Public Health Service Manning Feinleib, M. D., Dr. P. H., Director 

Centersfor DiseaseControl 
there was no trend with age 

among those 65 years of age 

and over. 

This report will first present 

information on the prevalence 

and coprevalence of nine 

common chronic conditions in a 

national sample of persons 

60 years of age and older. The 

impact of comorbidity will then 

be assessed by estimating the 

prevalence of disability in 

activities of daily living according to the number of conditions 

present. 

Materials and methods 

The National Health 

Interview Survey (NHIS) is the 

National Center for Health 

Statistics’ large continuing 

survey of the civilian noninstitutionalized population of the 

United States. Each year, 

people in about 42,000 households are interviewed by U.S. 

Bureau of the Census interviewers to obtain information about 

their health and use of health 

care. Demographic information 

that is needed to interpret the 

data is also obtained. The 

interviewers have special 

training for this survey, in 

addition to their regular 

training, and response rates are 

high-about 97 percent. The 

only item with a relatively low 

response rate is family income. 

In 1984 a special supplement was added to the questionnaire to obtain information 

about older people who were 

living in the community (3). 

This supplement, the Supplement on Aging (SOA), was 

designed to collect information 

about chronic conditions, 

physical limitations, housing, 

retirement status, interactions 

with family and organizations, 

use of community services, and 

other health-related and social 

information about people 

middle-aged and older. All 

household members 65 years of 

age and over and a one-half 

sample of those 55-64 years of 

age were asked the questions 

on the supplement themselves 

when possible. Another 

household member was 

interviewed only when the 

selected person was unable to 

answer either because of 

physical or mental problems or 

because of being away from the 

household for a longer period 

than the interviewer would be 

in the area. Response rates to 

the SOA were also high; 

95 percent of the people 

selected from the NHIS sample 

had complete interviews with 

the SOA. Overall, 91.5 percent 

of the SOA sample responded 

for themselves. There were 

16,148 persons interviewed in 

the SOA. The analyses presented here are for the 13,807 

individuals 60 years of age and 

3Fitti JE, Kovar MG. The supplement 

on aging to the 1984 National Health 

Interview Survey. National Center for 

Health Statistics.Vital Health Stat. 

1(21). 1987. 

older, representing an estimated 

37.3 million noninstitutionalized 

persons in this age range in the 

United States in 1984. 

All estimates in this report 

are based on the national 

estimates. All estimated 

variances and tests of significance take the complex sample 

design into account. The 

authors have taken care not to 

make statements about differences unless it is likely that the 

same differences would be 

found using the same techniques in a complete census. 

The list of chronic conditions used in the SOA was 

designed by selecting those 

conditions most prevalent 

among older people from the 

condition lists on the NHIS. 

Each participant was asked 

whether he or she had each 

condition. For 13 conditions, 

participants were asked if they 

had ever had the condition. For 

5 conditions (arthritis, diabetes, 

aneurysm, blood clots, and 

varicose veins), participants 

were asked if they had the 

condition in the past 12 

months. For the purpose of this 

report, the cataract category 

includes those saying they 

currently have a cataract, have 

had surgery for a catarac~ or 

have had a lens implant for a 

cataract. Heart disease was 

considered present in those who 

reported they had ever had 

coronary heart disease, angina 

pectoris, a myocardial 

infarction, or any other heart 
I 

attack. Osteoporosis and hip 

fracture were combined into 

one category. 

The prevalence of comorbidity is related to the length of 

the list of possible comorbid 

conditions. For the purpose of 

the analyses in this report, only 

nine common chronic conditions are considered. A longer 

list of conditions would 

obviously lead to a higher 

prevalence of comorbidity. One 

of the methodologic problems 

that makes the study of specific 

patterns of comorbidity difficult 

is that the number of combinations of conditions can grow 

very large. Even using this 

restricted list of 9 common 

conditions, there are 36 possible 

pairs of co-occurring conditions. 

If rarer conditions were 

included, the number of 

possible combinations would be 

much larger and the number of 

people in each cell would 

become too small for useful 

analysis. 

If two conditions are 

independent, their expected 

coprevalence is the product of 

their individual prevalence 

rates. For example, the expected coprevalence of arthritis 

and hypertension is 

(.490)(.418)(100) = 20.5 

percent. The observed coprevalence of two conditions was 

compared with the expected 

coprevalence, which was 

calculated on the assumption of 

independence of the conditions. 

The percent difference was 

calculated using the formula: 

((Observed - Expected)/ 

Expected) X 100 

The SOA included questions 

on six activities of daily living 

(ADL): bathing or showering, 

dressing, eating, getting in and 

out of bed or a chair, walking, 

and using the toilet. Participants 

were first asked if they had 

difficulty performing each of 

these activities. Those reporting 

difficulty were then asked how 

much difficulty and whether 

they received help from another 

person. This report provides 

information, according to the 

number of chronic conditions, 

on the proportion of people 

who have difficulty with one or 

more of these activities and the 

proportion receiving help from 

another person to perform one 

or more of the activities. 

Because the questions on 

ADL’s were asked separately 

from the questions on chronic 

conditions, the reader should 

not infer that these are necessarily the conditions that cause 

the ADL difficulty. 

Prevalence of chronic 

conditions 

The prevalence of the nine 

common self- or proxy-reported 

chronic conditions or groups of 

conditions in those 60 years of 

age and older that are considered in these analyses are 

shown in the following list. 

(AIzheimer’s disease was on the 

list but because less than 

Advance Data 3 

0.5 percent of respondents or 

their proxies reported this 

condition, it was not included in 

these analyses.) 

Percent of 

Condition population 

Arthritis . . . . . . . . . 49.0 

Hypertension . . . . . 41.8 

Cataracts . . . . . . . . 19.9 

Heart disease . . . . 14.0 

Varicose veins . . . . 9.9 

Diabetes . . . . . . . . 9.5 

Cancer (except 

nonmelanoma 

skin cancer) . . . . . 6.6 

Osteopxosis or 

hip fracture . . . . . . 5.5 

Stroke . . . . . . . . . . . 5.4 

Prevalence of comorbidity 

The proportion of the 

population with none of the 

nine chronic conditions or with 

four or more was higher than 

would have been expected by 

chance (table 1). 

The proportion of the 

population 60 years of age and 

older with two or more of the 

nine chronic conditions under 

consideration was higher at 

each older age and, for each 

age group, was higher for 

women than for men (figure 1). 

Table 1. Proportion of population 

observed and expected to have the 

specified number of chronic 

conditions, and ratio of observed to 

expected: United States, 1984 

Ratio 

of 

Number obsewed 

of Observed Ekpected to 

conditions percent percent expected 

o. . . . . . . . . 21.2 13.9 1.53 

1. . . . . . . . . 30.1 34.7 0.87 

2 . . . . . . . . . 25.9 32.3 0.80 

3 . . . . . . . . 14.6 14.7 0.99 

4. . . . . . . . . 6.0 3.7 1.62 

5 or more. . 2.3 0.6 3.83 
. . . .

4 Advance Data 

~. 2 chronic conditions ....... •l....... or more 

Izlfin

1 chronic condition 

O chronic conditions 

100 “ 

80 -

60 -

40 -

20 -

o— 

60-69 70-79 80 years 60-69 70-79 80 years 

years years and over years years and over 

Men Women 

Figure 1. Percent distribution of populat”wn 60 years of age and over by 

number of chronic condtiions, according to age group and sex: 

United States, 1984 

For those 80 years of age 

and older, 70 percent of the 

women and 53 percent of the 

men had two or more of the 

nine conditions. The prevalence 

of the eight most commonly 

occurring pairs of comorbid 

conditions is shown in figure 2. 

Prevalence of comorbidity for 

a pair of conditions is very 

much related to the prevalence 

of each of the individual 

conditions. High blood pressure 

and arthritis, the two conditions 

with the highest prevalence, 

co-occurred in 24.1 percent of 

those 60 years of age and older; 

cataract and arthritis were both 

reported by 11.7 percent. The 

remaining six pairs of common 

comorbid conditions had 

coprevalences of 5–10 percent. 

In each case, for the eight most 

common pairs of conditions, 

there was an increase in 

observed comorbidity over 

expected comorbidity in people 

60 years of age and older 

(figure 3). All increases, except 

for cataract with high blood 

pressure in men, were statistically significant at p <.001 in 

analyses that adjusted for the 

complex sampling design. 

Analyses of specific age groups 

show similar relationships. 

Relationship of 

comorbidity with disability 

The pe~ent of men and 

women having difficulty or 

receiving help with ADL’s, by 

number of chronic conditions, is 

shown in figure 4. There is a 

clear, graded increase in the 

proportion with disability of 

those with none of the nine 

conditions to those with five or 

more of the conditions. There is 

no consistent difference 

between men and women 

(within each stratum) of number 

of conditions. Since age and 

gender are related to the 

prevalence of comorbidity, data 

are presented for three separate 

age groups for men and women 

(figures 5 and 6; table 2). 

Again, within each age group 

there is a systematic increase in 

the percent with disability in 

ADL’s with increasing numbers 

of conditions. Looking across 

age groups for a specific 

number of conditions, there is 

also, in general, a graded 

increase in disability with 

increasing age. 

Discussion 

Analysis reveals that, using 

this list of nine commonly 

reported chronic conditions, the 

prevalence of comorbidity is 

substantial. High rates of 

comorbidity are seen for 

women, with prevalence rates 

rising from 45 percent in the 

age group 60-69 years to 70 

percent in those 80 years of age 

and older. 
Advance Data 5 

. 24.1 

. 

. 

. 

High blood Cataract Heart Varicose Diabetes Cataract Heart Diabetes 

pressure disease veins disease 

With arthritis With high blood pressure 

Figure 2. Prevalence of most common comorbid conditions among people 60 years of age and ove~ 

United States. 1984 

50 -

z! Men 

Izl Women 

40 -

% 30 - — 

.-E 

2 

8 

~ 20 

IL 

10 -

o— 

High blood Cataract Heart Varicose Diabetes Cataract Heart Diabetes 

pressure disease veins disease 

With arthrifs With high blood pressure 

People 60 years of age and over 

Figure 3. Percent increase in observed over expected frequency of most common comortid conditions among men 

and women 60 years of age and ove~ United States 1984 
. 

6 AdvanceData 

100 

Having difficulty in 1 or more In activities of daily living

Iz Receiving help in 1 or more 

activities of daily living 80 

[ 

60 

,40 

20 

0 

Men Women Men Women Men Women Men Women Men Women Men Women 

o 1 2 3 4 5 or more 

Number of chronic conditions 

Figure 4. Age-adjusted prevalence of men and wornen 60 yearn of age and over having difficulty and receiving help In 1 

or more activities of daily living, by number of chronic conditions: United Sfate% 1984 

100	r In Having difficulty in 1 or more 

activities of daily living 

0123 4 5or 0123 450r O 1 2 3 4 5or 

more more more 

Number of chronic conditions 

\	 figure 5. Prevalence of men 60 years of age and over having dficulty and receiving help in 1 or more activities of daify 

living, by number of chronic conditions and age group United States, 1984 
. 

Advance Data 7-

� Having difficulty in 1 or more 

activities of daily living 

Receiving help in 1 or more. 

z? activities of daily living 

Women 70-79 

years of age 

more more more 

Number of chronic conditions 

Figure 6. Prevalence of wornen 60 years of age and over having diiiulty and receiving heb in 1 or more activities of 

daily Wing, by number of chronic conditions and age group: United States, 1984 

Table 2, Percent of persons 60 years of age and over receiving help and having 

difficulty with 1 or more activities of daily living, by number of chronic 

conditions, sex, and age: United States, 1984 

Sex and age 

Men 

Ageadjusted, . . . . . . . . . . . . 

60-69 years of age ,.. . . . . . 

70-79 years of age . . . . . . . . 

80 years of age and over . . . 

Women 

Ageadjusted . . . . . . . . . . . . . 

60-69 years of age . . . . . . . . 

70-79 years of age . . . . . . . . 

80 years of age and over . . . 

Men 

Ageadjusted, . . . . . . . . . . . . 

60-69 years of age . . . . . . . . 

70-79 years of age . . . . . . . . 

80 years of age and over . . . 

Women 

Age adjusted . . . . . . . . . . . . . 

60-69 years of age . . . . . . . . 

70-79 years of age. . . . . . . . . 

80 years of age and over . . . 

Number of conditions 

o 1 2 3 4 5 or more 

Percent of population receiving help 

2.1 4.8 8.6 13.4 22.0 23.0 

1.3 2.9 6.3 10.7 19.1 23.3 

3.2 3.4 7.7 15.7 22.2 28.5 

2.9 15.7 20.2 17.0 31.4 49.8 

2.3 5.7 6.5 12.7 15.7 27.7 

1.4 3.9 4.2 10.1 12.0 21.0 

2.2 5.2 7.6 11.1 17.5 28.5 

6.5 14.4 16.9 27.4 37.5 58.1 

Percent of population having difficulty 

5.4 12.8 20.9 31.3 50.6 52.3 

3.6 8.9 16.9 30.4 50.4 45.2 

5.2 12.5 21.1 31.2 48.7 59.9 

13.3 29.2 36.6 32.7 51.5 87.0 

5.2 13.7 21.7 32.3 41.4 63.7 

3.0 10.5 17.0 26.8 33.9 60.6 

5.2 14.7 22.6 33.3 47.1 58.4 

14.0 24.4 38.8 52.0 66.9 79.2 

For the most commonly 

reported pairs of comorbid 

conditions, the observed 

coprevalence is consistently 

higher than the expected 

coprevalence. It was anticipated 

that high blood pressure and 

heart disease would co-occur at 

higher rates than expected from 

their individual prevalence rates 

because hypertension is a 

known risk factor for coronary 

heart disease. Likewise, high 

blood pressure and diabetes 

share an underlying risk factor, 

overweight, and it was anticipated that they would co-occur 

at higher rates than expected 

from their independent 

distributions. For the other six 

pairs of conditions, however, 

their rate of co-occurrence, 

*U. S. GO UERNIKNT PRINTING 0FFICC:1999-241 -2B1 :80026 
8 Advance Data 

ranging from 15 to 30 percent 

higher than expected, was not 

anticipated. While this is a 

modest increase in observed 

versus expected comorbidity, its 

impact on the total number of 

older Americans with specific 

patterns of comorbidity is 

substantial. For high blood 

pressure with arthritis, for 

example, the independent 

distributions of these two 

conditions would predict that 

7.6 million persons 60 years of 

age and older were living in the 

community with these two 

conditions. The estimate from 

the SOA is that there were 

9.0 million persons with this 

pair of conditions, about 

1.4 million more than expected. 

There are a number of 

possible explanations for the 

increase in observed versus 

expected coprevalence for 

conditions not generally 

recognized as being associated. 

Detection bias would likely 

have some effect, as those with 

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one condition may have more 

contacts with the medical care 

system and therefore greater 

likelihood of being diagnosed 

with a second condition. 

Individuals’ response patterns 

to questiomaires may also play 

a role. Those who acknowledge 

having one disease may be 

more likely to acknowledge 

having other diseases. 

Finally, there could be an 

underlying biological basis for 

these findings. In some individuals, genetic and environmental 

factors may increase general 

susceptibility to disease, 

resulting in the occurrence of 

multiple diseases in the later 

years of life. Assessment of this 

hypothesis would require a 

study that uses standardized 

medical diagnostic procedures 

and evaluates risk factors for 

general susceptibility, as 

evidenced by multiple chronic 

conditions. 

There was a very clear 

association found in these data 

between the number of 

conditions and the proportion 

of people with disability as 

assessed by ADL’s. This 

association was present even 

though no attempt was made to 

characterize the severity of the 

conditions, and despite the use 

of a list of conditions with 

potentially very different 

impacts on serious disability 

(for example, varicose veins and 

stroke). While these” are 

important limitations, the 

number of conditions appears 

to offer a useful measure of the 

burden of illness on the older 

individual, as judged by 

associated disability. 

Suggested citation 

GuralnikJM, LaCroix AZ, Everett DF, 

Kovar MG. Aging in the eighties: the 

prevalence of comorbidity and its 

association with disability. Advance 

data from vital and health statistics; 

no 170. Hyattsville, Maryland: 

National Center for Health Statistics. 

1989. 

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