Measurement Terminology and Locating Specific Measures

1. Class 2Measurement Terminology and Locating Specific MeasuresOctober 1, 2009 Anita L. Stewart Institute for Health & Aging University of California, San Francisco

2. Overview of Class 2 • Measurement terminology • Confusion, variation, and overlap • Items and response scales • Things to pay attention to in items • Locating measures • Finding literature on measures and measurement properties

3. Measurement • Assignment of numbers to: • aspects of objects/events according to a rule • an unobservable characteristic of individuals (construct/latent variable) • Numbers (measures) are “proxies” for the unobservable latent variable

4. Measurement of Latent Variables Variable A Measure A

5. Measurement of Latent Variables Variable A Item A1 Item A2 Item A3 Item A4

6. Measure of Energy/fatigue (“Vitality”) Energy/fatigue Feel tired Feel fullof pep Have a lotof energy Feel wornout

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

8. Types of Measurement Scales • Categorical • Classification • Numbers are simply labels for categories • Continuous • Ordinal • Interval • Ratio

9. Race/ethnicity: 1 African American 2 Asian 3 Latino 4 White 5 Other Health insurance:1 None 2 Private insurance 3 Medicare 4 MediCal Categorical Measures: Numbers Have No Inherent Meaning

10. Continuous vs. Classification Scores • Center for Epidemiological Studies Depression Scale (CES-D) • Continuous score (0-60) • 20 items on 0-3 scale are summed • Classification score (0-1) • Those scoring0-15 = 0 16-60 = 1 (likely to have depression)

11. Severity of pain: 1 None 2 Very mild 3 Mild 4 Moderate 5 Severe Income:1 < $10,000 2 $10,000 - <$20,000 3 $20,000 - <$30,000 4 >$30,000 Ordinal Scales: Numbers Reflect Increasing Level or Amount Numbers have no inherent meaning but indicate “more” or “less”

12. 1 – poor 2 – fair 3 – good 4 – very good 5 – excellent 0 = fair or poor 1 = good, very good, or excellent Ordinal vs. Categorical Scales In general, how would you rate your health?

13. Measure, Instrument, Battery, Questionnaire, Survey, Tool, Inventory • Measure - single- or multi-item scale or index (umbrella term) • Instrument - a published, named measure or set of measures • Battery - collection of measures from diverse sources

14. Questionnaire, Survey, Tool, Inventory • Questionnaire - any of the above (instrument, profile, battery) formatted into a set of measures • Survey - same as questionnaire • Tool = Questionnaire = Survey? • Inventory?

15. 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

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

17. Multidimensional and Unidimensional • A multidimensional “measure” has scores for each subdomain • Unidimensional measure • Only one score is obtained • Dimensionality must be empirically tested • e.g., factor analysis identifies number of factors or dimensions

18. Example of Unidimensional “Scale” • Perceived Stress Scale (PSS) • Single score from all items • 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 Cohen, S, J Health Soc Behav 24:385-396, 1983

19. Example of Multidimensional “Questionnaire” • Patient Satisfaction Questionnaire (PSQ) • 55 items, 18 subscales, e.g. • Access to care • Technical quality • Interpersonal manner • Explanations • Continuity of care Marshall GN et al., Psychol Assess, 5:477-483, 1993

20. Example of a Multidimensional “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 Also two summary indexes • Mental health component • Physical health component

21. Overview of Class 2 • Measurement terminology • Confusion, variation, and overlap • Items and response scales • Locating measures

22. Composition of an Item During the past month, how much of the time have you felt tired?1 Never 2 A little of the time 3 Some of the time 4 Most of the time 5 All of the time Itemstem Response scale

23. Things to Pay Attention to in Items • Item stem • Time frame • Complexity • Response scales • Type • Number of choices • Specific choices, distance between choices • Format • Match of response choices to item stem

24. Past: Present: No time frame: Average experience over some previous time period (6 months, 3 months, 4 weeks, etc) Current status - today, in general Time frame not specified Time Frame: Part of Concept Definition

25. Response Scale Choices: “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. Public Opinion Quart 1979, 92-101.

26. Example of Vague Quantifier For people speaking a language other than English at home: • How well does this person speak English? • Very well • Well • Not well • Not at all

27. Example of Vague Quanitifier For people speaking a language other than English at home: • How well does this person speak English? • Very well • Well • Not well • Not at all U.S. Census 2000! http://www.census.gov/dmd/www/pdf/07f_or.pdf

28. Types of Response Scales

29. State/level Evaluative Comparative Able/unable Extent of limitation Amount of difficulty Need for help Speed of completing defined task Satisfaction with level Level compared to others your age Change compared to one year ago Change compared to before treatment Types of Response Scales for Physical Functioning Items (e.g., walk, climb stairs)

30. Level/state Evaluative Comparative Had symptom (yes/no) Frequency Intensity/severity (usually, at its worst) Amount of time, # of days had it Extent to which bothered by Sx Extent of distress due to Sx Extent of change (e.g. frequency) since start of treatment Types of Response Scales for Symptoms Items (e.g., nausea, fatigue)

31. Variation Within State/Level Response Scales • Worry about health • Intensity (severity) of worry • Frequency of worry • Amount of time worried

32. 1 – Not at all 2 - Slightly 3 - Moderately 4 - Quite a bit 5 - Extremely 1 – Not at all 2 - A little 3 - A fair amount 4 - Much 5 - Very much Intensity Response Scale Choices In the past 4 weeks, how worried have you been?

33. 1 – Not at all 2 - A little 3 - Fairly 4 - Quite 5 - Extremely 1 – Not at all 2 - A little 3 - Somewhat 4 - Very much More Intensity Response Scale Choices In the past 4 weeks, how worried have you been?

34. 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 Frequency Response Scale Choices How often in the past 4 weeks have you been worried....

35. 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 More Frequency Response Scales How often in the past 4 weeks have you been worried....

36. 1 – None of the time 2 – A little of the time 3 – Some of the time 4 – Most of the time 5 – All of the time Amount of Time Response Scales How much of the time in the past 4 weekshave you been worried....

37. Feature of Ordinal Scales • Distances between numbers unknown, usually vary • some closer together in meaning than others

38. Interpretability of “Numbers” in Single Item Ordinal Scale Is “very good” (4)twice as goodas “fair” (2)?

39. Distance Between Levels: “In general, how would you rate your health?” Stewart and Ware, Measuring Functioningand Well-Being 1992, p. 299.

40. Distance Between Levels: “In general, how would you rate your health?” -- 20 -- largest diff -- 26 -- -- 18 -- -- 11 --

41. Distance Between Levels: “In general, how would you rate your health?” -- 20 -- -- 26 -- -- 18 -- smallest diff -- 11 --

42. Response Choice Formats • Numeric and non-numeric scales • verbal descriptors of all levels • verbal descriptors of endpoints only • verbal descriptors of endpoints plus midpoint • Visual analogue scale • 10cm line with endpoints labeled

43. Format: Numeric Scale with 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

44. Format: Non-Numeric Scale with Verbal Descriptors of All Levels  All of the time  Most of the time  Some of the time  A little of the time  None of the time

45. Format: Is This Numeric or Non-Numeric? 1All of the time 2Most of the time 3Some of the time 4A little of the time 5None of the time

46. Format: Bidirectional Numeric Scale, Endpoints and Midpoint Labeled -3 -2 -1 0 1 2 3 Very No Very much change much worse better

47. Visual Analogue Scale (VAS) 10 cm Line:A Non-Numeric Scale Pain asbad as you canimagine Nopain

48. How is a VAS measured? • Measure the distance from the “no pain” end in cm with a ruler • have to measure each survey by hand • Precision: measure to the nearest cm, rounding to achieve a whole number from 0-10 • or to nearest mm

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

50. Another Numeric Scale with 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