General Introduction to health measurement

1. General Introductionto health measurement (Note: I have added explanatory notes to many of the slides; to see these you will need to save the file and open in the ‘normal view’ mode)

2. Defining ‘Measurement’ “Measurement consists of rules for assigning numbers to observable attributes so as to represent quantities of the attributes” Oh gosh, let’s try to sort that out… • The “attributes” can refer to dimensions, properties, characteristics, or behaviors (e.g., weight, density, cost, physical function) • If it’s not observable, it’s not measurable (but for health, let’s define observable broadly: if they say they feel bad, you observed it). • “Operational definitions” indicate how to measure an attribute that is not directly observable (e.g., health, quality of care)

3. Classification of Health Measures • Measures can be classified by their purpose. For example: • Evaluative (e.g., outcome measures) • Diagnostic (e.g., BP, ESR) • Prognostic (e.g., Apgar; screening tests) • Discriminative (e.g., IQ tests) • Summary population measures (e.g., death rates)

4. Classification (2) 2. Or, measures may be classified descriptively: • Scope of the measure (e.g., specific or generic) • Qualitative vs. quantitative (some discussion needed here!) 3. Or methodologically: • Subjective vs. objective (how is the information collected?) • How administered (questionnaires; clinician ratings; laboratory tests) • Structured vs. semi-structured • How they are scored: indexes vs. profiles

5. Types of numerical scales Discrete vs. continuous variables: Mnemonic: NOIR

6. Ways to Present Scores • The raw scores • Single index value or profile • Norm-referenced: • Z-scores (or other types of standard scores : see next slide) • Percentiles • Criterion-referenced: • Pass/fail • Clinical diagnosis

7. Maybe the scale spacing should be presented like this, to “bell curve” it? Raw Scores 1-100 scale: e.g., 3MS scores Population distribution (Note: we tend to assume, but don’t really know, if the scale points are evenly spaced, as drawn)

8. What’s an “Index”? • “Standard, weighted, composite set of indicators” • ‘Weighted’ means that each element can receive a different salience in the overall score • ‘Composite’ means there’s some way to combine the elements • Gives a broad-spectrum indication of overall level of a complex attribute • Generally used for broad comparisons • Examples: consumer price index; hospital activity index; Health Utilities Index

9. Measuring vs. Classifying:some possible distinctions

10. Choosing Your purpose drives your choice. What type: Specific or generic? Objective or subjective? There are criteria for evaluating & comparing tests Off the peg, or design your own? Where do you get information on a scale? Applying Measures Practical issues: Interview or self-administered? Cost & difficulty How to score it? Analyzing scores Interpreting scores Choosing & Applying Measurements

11. Old ways of administering health questionnaires may not be practical • Face-to-face Interview $150 + • Telephone Interview $ 50 + • Self-administered postal $ 20 + • Computerized via Web $ <5? (US $)

12. Cone of Measurement Demands:How much effort does it require of the respondent? IQ tests, etc . HRQOL . ADLs . . . . EKGs Very demanding:lower responserate? Minimal effort

13. Practical issue: abbreviated versions Broad spectrum, but coarse discrimination:may not show changes Measure too low (“ceiling effect”)but has gooddiscrimination The ideal scale (broad range + fine discrimination:band widthand fidelity) Short Forms (same number of items) (Source: John Ware, October 2000)

14. Match the Instrument to the Application Population Monitoring Outcomes Research Patient Management 4 4 4 3 3 3 2 2 2 1 1 1 Source: John Ware, October 2000