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 1 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’) • • • • Eye and vision conditions Hearing problems Hypertension Diabetes Subdimensions… • • • • • • • 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 2 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 3 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’ 4