Composite Measures:
The Total Illness Burden Index
Sheldon Greenfield, MD
Donald Bren Professor of Medicine
UC Irvine School of Medicine
Academy Health Annual Meeting
June 5, 2007
Total Illness Burden:
The Latent Construct
• Hypothesized construct = composite
illness-based measure of risk for
substantial declines in health (1-5 years
post initial observation)
Rationale
• Composite measure of severity of multiple
illnesses, conditions is needed to:
– Adjust comparisons for case-mix
– Inform treatment decisions
• Existing measures:
– Based on diagnoses, often not available,
accurate
– Don’t deal with cumulative severity of
illnesses
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To Address Issues…
• Developed composite measure of ‘total
illness burden’ based on:
– Clinically defined, multi-item severity
measures
– ~15 conditions, 88 items
– Variable based on index condition
– Psychometric testing for reliability, validity
Subdimensions (cont’)
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Eye and vision conditions
Hearing problems
Hypertension
Diabetes
Subdimensions…
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Pulmonary disease
Heart disease
Stroke and neurologic disease
Gastrointestinal conditions
Other cancers (excluding prostate)
Arthritis
Foot and leg conditions
Sample Questions: COPD
1. During the past 6 months, how often did
you have wheezing?
a. Never
b. Once or twice
c. About once a week
d. Several times a week
e. Several times a day
Sample Questions: COPD
Sample Questions: COPD
2. During the past 6 months, how often did
you feel short of breath? (Always, Usually,
Sometimes, Rarely, Never)
a. When lying down flat
b. When sitting or resting
c. When walking less than one block
d. When climbing one flight of stairs
e. When climbing several flights of stairs
3. When you coughed during the past 6
months, how much phlegm or sputum
did you cough up?
a.
b.
c.
d.
e.
None
Less than a teaspoon a day
About a tablespoon
Several tablespoons
About a cup or more a day
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Sample Questions: COPD
Sample Questions: COPD
4. During the past 6 months, did you use
extra pillows in order to sleep at night
because of problems with your breathing?
a. No
b. Yes, 1 pillow
c. Yes, 2 pillows
d. Yes, 3 or more pillows
5. During the past 6 months, how many different
times did you have each of the following?
(Never, Once, Twice, Three or more times)
a. Pneumonia
b. Bronchitis, for which
you took antibiotics
c. Flu, with coughing
Sample Questions: COPD
6. Have you ever been told by a physician
that you have any of the following
problems with your breathing?
Yes
No
a. Emphysema …………
b. Chronic bronchitis …...
c. Asthma ……………….
Steps in Constructing Subdimensions
• Transformed variables to uniform metric
• Tested reliability of clinically defined
scale (Cronbach’s alpha > .80)
• Created composite of each subdimension
using simple algebraic sum, mean
• Items in each subdimension varied
• Validated each subdimension as scale
using SF-36, etc.
Steps in Constructing Composite
• Conducted principal components
analysis, higher order factor analysis
using scales as entries
• First factor explained 67% of variance
• Other factors had Eigen values, scree
indicating single factor solution
• Factor loadings ranged from .40 - .70
• Used factor loadings to create composite
• Validated derived composite
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Conclusions
• Principal components analysis, factor
analysis, possible to derive latent
construct that reflects patients’ “total
illness burden”
• To be useful in clinical decision making,
future research aimed at improving
sensitivity, specificity, particularly at
‘intermediate ranges’
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