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Class 2 Measurement Terminology and Locating Measures October 6, 2005

Class 2 Measurement Terminology and Locating Measures October 6, 2005. Anita L. Stewart Institute for Health & Aging University of California, San Francisco. From Last Week. Some information based on last week’s discussion On weights and values

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Class 2 Measurement Terminology and Locating Measures October 6, 2005

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  1. Class 2Measurement Terminology andLocating MeasuresOctober 6, 2005 Anita L. Stewart Institute for Health & Aging University of California, San Francisco

  2. From Last Week • Some information based on last week’s discussion • On weights and values • Does cognitive functioning reflect physical health?

  3. Implicit and Explicit “Weighting” • Description (describe health states) • Valuation (mapping those health states onto a set of values) • Most measures use “implicit” values • Utility or preference measures represent “explicit” values Kind P. Values and valuation in the measurement of HRQoL, in P Fayerset al (eds) Assessing quality of life in clinical trials, 2nd ed, Oxford, 2005

  4. Example of “Implicit” Weighting: Number of Items per Domain in 3 MOS Indexes

  5. Example of “Implicit” Weighting: Percent of Items per Domain in 3 MOS Indexes

  6. Correlations of MOS Long Form Measures with Physical and Mental Health Hays RD and Stewart AL, The structure of self-reported health inchronic disease patients, Psychol Assessment, 1990;2:22-30.

  7. Overview of Class 2 • Measurement terminology • Confusion, variation, and overlap • Types of response scales, contribution to concept definition • Measurement models • Depicting structure of measures • Locating measures

  8. Measurement • Assignment of numbers to aspects of objects or events according to a rule • Assignment of numbers to an unobservable characteristic of individuals (construct)

  9. Construct, Concept, Variable, Latent Trait, Latent Variable • Terms defined differently by different investigators/authors • Meaning is very similar • considerable overlap among them, • Often used interchangeably

  10. Construct/Concept • A variable that is relatively abstract as opposed to concrete and is defined or operationalized in terms of observed indicators • An idea developed or constructed through informed scientific theory. Concepts that are directly or indirectly observable. • An abstraction based on observations of certain behaviors or characteristics (e.g. pain, stress)

  11. Latent Trait, Factor • Latent - present but not visible, unobservable • Latent trait - unobservable set of characteristics that can be empirically inferred and estimated through answers to a set of questions(Medical Care glossary) • Factor - a latent variable or theoretical construct operationalized in terms of associations among indicators in a factor analysis(Stewart and Ware, 1992 glossary)

  12. Latent Variable, Manifest Variable • Latent variable - unobservable latent trait given a label • Manifest variable is the “observed” information, i.e., the answers to items used to infer the latent trait

  13. Domain, Dimension, Sub-domain, Component • Domain: a state, attitude, perception, behavior, or other sphere of action or thought related to health …. All entities in a single domain have some property in common …. (Patrick & Erickson, 1993) • Dimension: a distinct component of a multidimensional construct that can be theoretically or empirically specified (e.g., physical and mental health)(Stewart & Ware, 1992, glossary)

  14. Example: Dimension, Component, Sub-domain • Mental health (dimension) • Psychological distress (component) • Depression (sub-domain) • Anxiety • Psychological well-being • Positive affect • Sense of belonging

  15. Components of Domains of MOS Long-form Measures • Role Role limitations due to:Functioning -- physical health -- emotional problems • Social Social limitations due to healthFunctioning Sexual problems Family functioning Marital functioning • Pain Pain severity Effects of pain Days with pain

  16. Multidimensional and Unidimensional • A multidimensional “measure” or “instrument” provides several scores • A “profile” of scores • Unidimensional measure - all items measure only one concept • Only one score is obtained • Dimensionality must be empirically tested • e.g., factor analysis identifies one factor,or more than one factor

  17. Example of Multidimensional Instrument • Patient Satisfaction Questionnaire (PSQ) • 55 items, 18 subscales, e.g. • Access to care • Technical quality • Interpersonal manner • Explanations • Continuity of care Marshall, GN Psychological Assessment, 5:477-483, 1993

  18. Example of Unidimensional Measure • Perceived Stress Scale (PSS) • 14 items, subjective experiences of stress • felt confident could handle life’s problems • able to control irritations in your life • difficulties piling up so high, could not overcome them • Single score from all items Cohen, S, J Health Soc Behav 24:385-396, 1983

  19. Instrument, Profile, Battery, Measure, Questionnaire, Survey, Tool, Inventory • Instrument - typically refers to a published, named measure or set of measures • Profile - same, but all scores on the same metric and can be compared (0-100 scales) • Battery (of independent measures) • collection of measures from diverse sources • Measure - single- or multi-item scale or index (umbrella term)

  20. Example of a Multidimensional Profile Instrument: SF-36 Measures 8 health concepts (36 items): • Physical functioning • Role limitations due to physical health • Role limitations due to emotional problems • Social functioning • Pain • Vitality (energy/fatigue) • Mental health • Health perceptions

  21. Generic vs. Disease-Specific Approaches • Generic • Applicable across many conditions anddiseases (e.g., sleep, health perceptions, fatigue, pain) • Disease-specific • Specific to particular disease or condition(e.g., arthritis, cancer, depression) • Generic approach (e.g., general dexterity scale for arthritis study) • Specific (nausea due to chemotherapy, back pain)

  22. Generic or Disease Specific bySingle Domain, Profile, or Index

  23. Questionnaire, Survey, Tool, Inventory • Questionnaire - any of the above formatted into a “questionnaire” or set of measures • Survey - same as questionnaire • Tool = Questionnaire = Survey? • Inventory?

  24. Examples of Names of “Instruments” • SF-36 Short Form Health Survey • Beck Depression Inventory • Health Assessment Questionnaire • Sickness Impact Profile • Center for Epidemiological Studies Depression Scale

  25. Example of a Battery • A survey for a particular study containing the following measures/instruments: • SF-36 (8 domains) • Perceived stress scale (1 domain) • Social support survey (4 domains) • Pain measure • Typical in clinical trials, epidemiological studies • Each measure serves particular purpose (outcome, predictor, mediator, covariate)

  26. Measure, Scale, Index, Item • Measure - single- or multi-item scale or index (umbrella term) • Scale - aggregation of items from one concept or domain, scored according to an accepted scaling method • Index - aggregation of 2 or more scales into a summary score • Item - a single question or statement including its response scale

  27. Item • Consists of an item stem and a response scale or response choices • Item stem – • The question or statement • Response scale or choices – • Answers presented to a respondent with which to respond to a (closed-ended) question

  28. Example of a Response Scale How often have you felt tired inthe past week?1 Never 2 Once or twice 3 A few times 4 Fairly often 5 Very often Itemstem Response scale

  29. Response Choice Formats • Verbal descriptors of all levels • Verbal descriptors of endpoints only • Verbal descriptors of endpoints plus midpoint • Visual analogue scales: 10cm line with endpoints labeled

  30. Format: Verbal Descriptors of All Levels 1 - All of the time 2 - Most of the time 3 - Some of the time 4 - A little of the time 5 - None of the time

  31. Vague, Imprecise Quantifiers • How often? • very often, pretty often, not too often • Sometimes, often, never • How much? • Too little, about right, too much • Below average, average, above average Bradburn NM, Vague quantifiers. Public Opinion Quart 1979, 92-101.

  32. Intensity Scales – “How distressed have you been?” • Not at all, slightly, moderately, quite a bit, extremely • Not at all, a little, a fair amount, much, very much • Not at all, a little, fairly, quite, very, extremely • Not at all, a little, somewhat, very much

  33. 1 - Never 2 - Once or twice 3 - A few times 4 - Often 1 – Never 2 - Hardly ever 3 - Some days 4 - Most days 5 - Almost every day 6 - Always, every day “How Often” Response Scales

  34. 1 - Never 2 - Almost never 3 - Sometimes 4 - Fairly often 5 - Very often 6 - Always 1 - Once or twice 2 - A few times 3 - Fairly often 4 - Very often 5 - Almost every day 6 - Every day “How Often” Response Scales

  35. Format: Verbal Descriptors of Endpoints Only 0 1 2 3 4 5 6 7 8 9 10 No Pain painas bad as you can imagine

  36. Format: Verbal Descriptors of Endpoints with Midpoint Labeled Very Very much 1 2 3 4 5 6 7 much worse No better change

  37. Format: Verbal Descriptors of Endpoints with Midpoint Labeled -3 -2 -1 0 1 2 3 Very No Very much change much worse better

  38. Format: Visual Analogue Scale, 10 cm Line No Pain pain as bad as you can imagine

  39. Optimal Number of Response Choices • Are 100 levels better than 5 or 10? • 5-points is probably optimal for respondents • Especially if items will be combined into multi-item scales • For single-item measures • 7 points may be preferred • Allows distribution over 5 points since peopleseldom use endpoints • Hard to come up with labels for 7-point scales

  40. Format: Verbal Descriptors of Endpoints Only 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 No Pain pain as bad as you can imagine

  41. Magic Number 7 + 2 • George Miller determined that 7 “chunks” of information is the most that short-term memory can retain • Plus or minus two (5-9 possible) • Seven (+ 2) is also the most points that people can discriminate along a continuum • Principle has held up well in measurement Miller, GM Psychological Bulletin, 63:81-97, 1956

  42. 1 - Not at all active 2 - A little bit active 3 - Moderately active 4 - Quite active 5 - Extremely active 1 - Not at all active 2 - A little active 3 - Fairly active 4 - Quite active 5 - Very active 6 - Extremely active Can You Make a 7-point Intensity Scale? (How physically active were you this week?)

  43. Measurement Models • The dimensional structure of a measure in terms of how the items related to the constructs (latent traits, factors, concepts) • Can be depicted as a list or visually • Standard visual format for structural equation modeling (SEM)

  44. Measurement Models • Physical Functioning (4 items) • Psychological Distress (7 items)

  45. Measurement Model (List format) • Physical Functioning defined in terms of: • Walking • Climbing stairs • Bending • Reaching

  46. Measurement Model (Visual format) Physical Functioning Reaching Climbing Stairs Bending Walking

  47. Measurement Model (List format) • Psychological distress • Depression • Sad • Lost interest • Can’t get going • Anxiety • Restless • Nervous

  48. Measurement Model (Visual format) Psychological Distress Depression Anxiety Sad Lost interest Can’t get going Restless Nervous

  49. What’s in a Label? • Don’t be fooled

  50. Content Areas: Four Depression Measures

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