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General Introduction

General Introduction. Some Notes. Definition of Measurement. “Measurement consists of rules for assigning numbers to observable attributes so as to represent quantities of the attributes”

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General Introduction

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  1. General Introduction Some Notes

  2. Definition of Measurement “Measurement consists of rules for assigning numbers to observable attributes so as to represent quantities of the attributes” • “Attributes” can mean dimensions, properties, characteristics, or behaviors (e.g., height, density, cost, physical function) • If it’s not observable, it’s not measurable (but let’s define observable very broadly). • “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 may be classified by their purpose: • Evaluative (e.g., outcome measures) • Diagnostic (e.g., BP, ESR) • Prognostic (e.g., Apgar; screening tests) • Discriminative (e.g., IQ tests) • Measures for Individuals or Groups

  4. Classification (2) 2. Measures may be classified descriptively: • Scope of the measure (e.g., specific or generic) • Qualitative vs. quantitative 3. Or methodologically: • Subjective vs. objective • How administered (questionnaires, rating scales) • Structured vs. semi-structured • How they are scored: indexes vs. profiles

  5. Scale Types Discrete or continuous variables • Nominal (e.g., sex; blood type). You can count these • Ordinal (house numbers; “mild pain”). <, > apply • Interval (C; Jan. 9, 2005). You can add, subtract • Ratio (weight; BP; # doctor visits). You can multiply & divide these (Mnemonic: NOIR)

  6. What’s an Index? • Standard, weighted composite set of indicators • Gives a broad-spectrum indication of general level of the attribute • Generally used for broad comparisons • Examples: consumer price index; hospital activity index; Health Utilities Index

  7. Choosing Criteria for evaluating a test Off the peg, or design your own? Where do you get information on it? What type: Specific or generic? Objective or subjective? Using Measures: Practical issues Interview or self-administered? How to scoring it? Analyzing scores Interpreting them Choosing & Using Scales

  8. Old Ways of Administering Health Questionnaires Are Not Practical • Face-to-face Interview $200 + • Telephone Interview $ 50 + • Self-administered $ 20 + • Computerized via Web $ <5?

  9. Cone of Measurement Demands:How much effort does it require of the respondent? IQ tests, etc . HRQOL . ADLs . . . . EKGs

  10. The Ideal Measurement and the Dilemma of Short Forms Broad spectrum, but too few marks (low discrimination) 3 Measure too low (ceiling effect) 2 2 1 1 The Ideal Short Forms (same number of items) (Source: John Ware, October 2000)

  11. 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

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