General Introduction

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 its not observable, its not measurable (but
  lets 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). lt, gt apply
• Interval (?C Jan. 9, 2005). You can add,
  subtract
• Ratio (weight BP doctor visits). You can
  multiply divide these
• (Mnemonic NOIR)

6
Whats 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 Using Scales

• 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

8
Old Ways of Administering Health Questionnaires
Are Not Practical

• Face-to-face Interview 200
• Telephone Interview 50
• Self-administered 20
• Computerized via Web lt5?

9
Cone of Measurement DemandsHow 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