Healthrelated Quality of Life: Application and Utility as an Outcome Measure in Primary Care Researc

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Health-related Quality of LifeApplication and
Utility as an Outcome Measure in Primary Care
Research

• Alvah R. Cass, MD, SM
• Department of Family Medicine
• University of Texas Medical Branch

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Workshops Objectives

• Describe the key elements of health services
  research and outcomes research
• Describe the elements critical in measuring
  health-related quality of life
• Evaluate and select a health-related quality of
  life instrument appropriate to your research
  question
• Define the minimum data set when conducting
  health-related quality of life research

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What is Health Services Research?
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Committee on Health Services Research

• Health services research is a multi-disciplinary
  field of inquiry, both basic and applied, that
  examines the use, cost, quality, accessibility,
  delivery, organization, financing, and outcomes
  of health care services to increase knowledge and
  understanding of the structure, processes, and
  effects of health services for individuals and
  populations. (Field, MJ et al. 1995)

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What is Outcomes Research?
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Agency for Healthcare Research and Quality (AHRQ)

• Outcomes research is a multidisciplinary
  endeavor that assesses the end results of health
  services that are important to the people who
  experience them. (Clancy CM and Eisenberg JM,
  1997)

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Patient Oriented Outcomes

• The best measure of quality is not how well or
  how frequently a medical service is given, but
  how closely the result approaches the fundamental
  objectives of prolonging life, relieving
  distress, restoring function and preventing
  disability. (Lembcke 1952)

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What is Health?
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World Health Organization (WHO)

• Health is a state of complete physical, mental,
  and social well-being and not merely the absence
  of disease or infirmity.

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What is Quality of Life?
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Quality of Life

• Health Issues
• Physical well-being
• Symptomatology
• Emotional well-being
• Primary
• Secondary
• Role-functioning
• Concept of impaired, disabled, handicapped

• General Issues
• Economic resources
• Human rights and freedoms
• Living conditions
• Personal
• Environmental

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What is Health-relatedQuality of Life?
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A Synthesis of Ideas

• Health-related quality of life is a concept that
  attempts to combine objective measurements of
  functional capacity across various health domains
  (health status) with measurements that represent
  an individuals subjective perception of health
  or sense of well-being. (Cass, 2001)

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Is HRQL the Right Construct?

• Objectives of quality healthcare
• prolonging life
• relieving distress
• restoring function
• preventing disability

• Measurement of health-related quality of life
• functional capacity across various health domains
• subjective perception or sense of well-being.

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Classification Scheme Muldoon
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Why Measure HRQL

• Impact of chronic disease
• Weak correlation between physiologic measures and
  functional measures
• Variation in response to disease
• Utilization of health care services and resources

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Goals of HRQL Measurement

• Differentiation
• Who has better HRQL compared to poorer HRQL?
• Evaluation
• How much change in HRQL has occurred?
• Prediction or Stratification
• Given current level of HRQL, what will happen in
  the future?

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Measurement Issues

• Reliability/Reproducibility
• Sensitivity to Change/Differences
• Validity/Accuracy
• Interpretability

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Signal to Noise

• Evaluation
• Responsiveness - ability to detect change
• Signal - magnitude of difference in HRQL in
  patients who change
• Noise - magnitude of fluctuation in HRQL in
  patients who do not change

• Differentiation
• Reliability - detects variability between vs.
  within subjects
• Signal - variability between subjects
• Noise - variability within subjects

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Validity

• Evaluation
• Correlations of changes in measures during a
  period in time
• Consistent with predictions from conventional
  wisdom

• Differentiation
• Correlations between measure at a point in time
• Consistent with predictions from conventional
  wisdom

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Interpretability

• Evaluation
• Quantify/Interpret differences within patients
  over a period of time
• trivial
• small
• moderate
• large

• Differentiation
• Quantify/Interpret differences between patients
  at a point in time
• trivial
• small
• moderate
• large

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Classification of Health Measurements

• Functional
• purpose or application of method
• Descriptive
• scope of the method
• Methodological
• technical aspects of the method

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Theoretical Underpinnings

• Psychophysics
• studies subjective judgments of stimuli that may
  be objectively measured
• much of this work is based on the power law
  expressed
• R k Sb

• Psychometrics
• studies use of subjective judgments when no
  objective, physical method to measure the
  phenomenon in question exists
• issues of scaling
• issues of rater-bias

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HRQL Instruments

• Generic instruments
• Health profiles
• Utility measures
• Specific instruments
• Disease specific
• Population specific
• Function specific
• Condition or problem specific

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Health Profiles

• Strengths
• Single instrument
• Detect differential effects on different aspects
  of health
• Comparison across interventions or conditions

• Weaknesses
• May not focus adequately or area of major
  interest
• May not be responsive

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Utility Measures

• Strengths
• Single value representing net impact on quantity
  and quality of life
• Cost-utility cost/effectiveness analysis possible
• Can incorporate states such as death

• Weaknesses
• Inherent difficulties in measuring utilities
• May not adequately measure different aspects of
  quality of life
• multi-attribute measures

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Disease Specific Instruments

• Strengths
• May be more sensitive to differences between
  groups and across time
• Face validity clinically sensibility

• Weaknesses
• Limits comparisons across conditions
• May be limited to population characteristics
• Responsiveness may be limited based on
  intervention

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Issues to Consider in Selecting an Instrument to
Measure HRQL
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Sensitivity to Change/Differences

• Measure differences between groups of dissimilar
  attributes
• Measure differences over time in groups of
  similar attributes as the condition changes over
  time
• Ceiling and floor phenomena
• Sensitivity to variation in groups of similar
  attributes

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Reliability

• Reliability
• Measurement variation
• Biological variation
• Precision
• Sensitivity
• Specificity

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Bias in Health Measurement

• Bias
• responses that depart systematically from the
  true values

• Response bias
• personality traits
• social desirability
• Interpretation bias
• extremes vs. middles
• Hello-good-bye effect
• Rebound effect

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Bias in Health Measurement

• Inclusive strategy
• accepts bias as part of the patients perception
• inherent bias does not effect validity
• consideration of the whole patient is hallmark
  of good care

• Exclusive strategy
• disentangle bias from reality
• disguise intent of question
• surrogate responders
• explicit rating of source of bias
• signal detection theory

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Validity

• Validity measures whether an instrument measures
  what it is intended to measure
• When a standard exists
• Criterion validity
• When a standard does not exist
• Face validity
• Construct validity
• Content validity

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Standards Exist

• Criterion validity - Does this instrument fit
  with empiric data?
• Concurrent - criterion refers to a current
  assessment
• Predictive - criterion refers to future
  assessment

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Standard Does Not Exist

• Face validity
• Taken at face value does this instrument measure
  health-related quality of life?
• Content validity
• Construct validity
• Convergent validity - sensitivity
• Discriminant validity - specificity

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Content Validity

• Content validity
• requires careful review of concept(s) to be
  measured
• careful review of previous works and studies
• relies on judgment of adequacy of item pool
• Is each concept represented?
• Are a sufficient number of items included for
  each concept?

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Construct Validity

• Construct - theoretically derived concept of the
  domain(s) to be measured
• provides expectations of measurement performance
• involves comparison between measures
• examines logical relations between a measure and
  the characteristics of population

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Minimum Data Sets Case-mix Adjustments

• Demographics
• Age, gender, ethnicity
• Spirituality
• Marital status
• Socioeconomic indicators
• Income, education, employment
• Comorbidity
• One size may not fit all

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Assumptions and Pitfalls

• Individuals can separate quality of life into
  health-related and non-health-related components
• Quality of life can be defined by a finite number
  of domains
• physical, emotional, and social functioning
• Life satisfaction or perception of well-being
  change over time and may not correlate with
  health status

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An Example The Short-Form 36 Instrument
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Background

• Health Insurance Experiment
• to construct best possible scales for measuring a
  broad array of functional and well-being concepts
  for non-aged adults and children
• Medical Outcomes Study
• provided a large scale test of the feasibility of
  self-administered patient questionnaires and
  generic health scales for those with chronic
  illnesses

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Scales of the SF-36

• Physical Functioning
• Role Physical
• Bodily Pain
• General Health

• Vitality
• Social Functioning
• Role Emotional
• Mental Health

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SF-36 Scales Health Phenomena
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SF-36 Scales General Population
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SF-36 Scales Gender Difference
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SF-36 Scales Age Differences
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SF-36 Scales Income Differences
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SF-36 Scales CHF
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SF-36 Scales for COPD/Asthma
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SF-36 Scales Chronic Arthritis
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SF-36 Scales Mood Disorders