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Reliability and Validity. Criteria of Measurement Quality. How do we judge the relative success (or failure) in measuring various concepts? Reliability – consistency of measurement Validity – confidence in measures and design. Reliability and Validity. Reliability focuses on measurement

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criteria of measurement quality
Criteria of Measurement Quality
  • How do we judge the relative success (or failure) in measuring various concepts?
    • Reliability – consistency of measurement
    • Validity – confidence in measures and design
reliability and validity3
Reliability and Validity
  • Reliability focuses on measurement
  • Validity also extends to:
      • Precision in the design of the study – ability to isolate causal agents while controlling other factors
        • (Internal Validity)
      • Ability to generalized from the unique and idiosyncratic settings, procedures and participants to other populations and conditions
        • (External Validity)
reliability
Reliability
  • Consistency of Measurement
    • Reproducibility over time
    • Consistency between different coders/observers
    • Consistency among multiple indicators
  • Estimates of Reliability
    • Statistical coefficients that tell use how consistently we measured something
measurement validity
Measurement Validity
  • Are we really measuring concept we defined?
    • Is it a valid way to measure the concept?
  • Many different approaches to validation
    • Judgmental as well as empirical aspects
key to reliability and validity
Key to Reliability and Validity
  • Concept explication
    • Thorough meaning analysis
  • Conceptual definition:
    • Defining what a concept means
  • Operational definition:
    • Spelling out how we are going to measure concept
four aspects of reliability
Four Aspects of Reliability:
  • 1. Stability
  • 2. Reproducibility
  • 3. Homogeneity
  • 4. Accuracy
1 stability
1. Stability
  • Consistency across time
    • repeating a measure at a later time to examine the consistency
    • Compare time 1 and time 2
2 reproducibility
2. Reproducibility
  • Consistency between observers
  • Equivalent application of measuring device
    • Do observers reach the same conclusion?
    • If we don’t get the same results, what are we measuring?
      • Lack of reliability can compromise validity
3 homogeneity
3. Homogeneity
  • Consistency between different measures of the same concept
    • Different items used to tap a given concept show similar results – ex. open-ended and closed-ended questions
4 accuracy
4. Accuracy
  • Lack of mistakes in measurement
  • Increased by clear, defined procedures
    • Reduce complications that lead to errors
  • Observers must have sufficient:
    • Training
    • Motivation
    • Concentration
increasing reliability
Increasing Reliability
  • General:
    • Training coders/interviewers/lab personnel
    • More careful concept explication (definitions)
    • Specification of procedures/rules
    • Reduce subjectivity (room for interpretation)
  • Survey measurement:
    • Increase the number of items in scale
    • Weeding out bad items from “item pool”
  • Content analysis coding:
    • Improve definition of content categories
    • Eliminate bad coders
indicators of reliability
Indicators of Reliability
  • Test-retest
    • Make measurements more than once and see if they yield the same result
  • Split-half
    • If you have multiple measures of a concept, split items into two scales, which should then be correlated
  • Cronbach’s Alpha or Mean Item-total Correlation
reliability and validity14
Reliability and Validity
  • Reliability is a necessary condition for validity
    • If it is not reliable it cannot be valid
  • Reliability is NOT a sufficient condition for validity
    • If it is reliable it may not necessarily be valid
  • Example:
    • Bathroom scale, old springs
types of validity
Types of Validity
  • 1. Face validity
  • 2. Content validity
  • 3. Pragmatic (criterion) validity
    • A. Concurrent validity
    • B. Predictive validity
  • 4. Construct validity
    • A. Testing of hypotheses
    • B. Convergent validity
    • C. Discriminant validity
face validity
Face Validity
  • Subjective judgment of experts about:
    • “what’s there”
    • Do the measures make sense?
  • Compare each item to conceptual definition
    • Do it represent the concept in question?
      • If not, it should be dropped
    • Is the measure valid “on its face”
content validity
Content Validity
  • Subjective judgment of experts about:
    • “what is not there”
  • Start with conceptual definition of each dimension:
    • Is it represented by indicators at the operational level?
    • Are some over or underrepresented?
  • If current indicators are insufficient:
    • develop and add more indicators
  • Example--Civic Participation questions:
    • Did you vote in the last election?
    • Do you belong to any civic groups?
    • Have you ever attended a city council meeting?
    • What about “protest participation” or “online organizing”?
pragmatic validity
Pragmatic Validity
  • Empirical evidence used to test validity
    • Compare measure to other indicators
  • 1. Concurrent validity
    • Does a measure predict simultaneous criterion?
      • Validating new measure by comparing to existing measure
      • E.g., Does new intelligence test correlate with established test
  • 2. Predictive validity
    • Does a measure predict future criterion?
      • E.g., SAT scores: Do they predict college GPA?
construct validity
Construct Validity
  • Encompasses other elements of validity
  • Do measurements:
    • A. Represent all dimensions of the concept
    • B. Distinguish concept from other similar concepts
  • Tied to meaning analysis of the concept
    • Specifies the dimensions and indicators to be tested
  • Assessing construct validity
    • A. Testing hypotheses
    • B. Convergent validity
    • C. Discriminant validity
a testing hypotheses
A. Testing Hypotheses
  • When measurements are put into practice:
    • Are hypotheses that are theoretically derived, supported by observations?
      • If not, there is a problem with:
        • A. Theory
        • B. Research design (internal validity)
        • C. Measurement (construct validity?)
  • In seeking to examine construct validity:
    • Examine theoretical linkages of the concept to others
      • Must identify antecedent and consequences
        • What leads to the concept?
        • What are the effects of the concept?
b convergent validity
B. Convergent Validity
  • Measuring a concept with different methods
    • If different methods yield the same results:
      • than convergent validity is supported
    • E.g., Survey items measuring Participation:
      • Voting
      • Donating to money to candidates
      • Signing petitions
      • Writing letters to the editor
      • Civic group memberships
      • Volunteer activities
c discriminant divergent validity
C. Discriminant (Divergent) Validity
  • Measuring a concept to discriminate that concept from other closely related concepts
    • E.g., Measuring Maternalism and Paternalism as distinct concepts
dimensions of validity for research design
Dimensions of Validity for Research Design
  • Internal
    • Validity of research design
      • Validity of sampling, measurement, procedures
  • External
    • Given the research design, how valid are
      • Inferences made from the conclusions
      • Implications for real world
internal and external validity in experimental design
Internal and External Validity in Experimental Design
  • Internal validity:
    • Did the experimental treatment make a difference?
      • Or is there an internal design flaw that invalidates the results?
  • External validity:
    • Are the results generalizable?
      • Generalizable to:
        • What populations?
        • What situations?
  • Without internal validity, there is no external validity