Validity and Reliability in Research Design

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					Validity and Reliability in
Instrumentation


47.469: Research I: Basics
Dr. Leonard
February 24, 2010
Recap
 Research design can be…
      experimental or non-experimental (maybe quasi-experimental)
      basic or applied research
      laboratory or field setting
      quantitative or qualitative data collection

 Research must be based in solid theory and testable
  hypotheses

 Research must include clear conceptual and operational
  definitions
Quasi-experimental
 Occurring more commonly in psychology

 Apply experimental principles like cause and effect or
  group comparison to field, or less controlled settings
    More like correlational research


 Less control over extraneous variables but can take place
  outside of lab, which may decrease the artificial feeling

 Interpretation of results not as clean as in experimental
  research but closer to “real world” application
  Scientific method
1. Formulate theories √

2. Develop testable hypotheses (operational definitions) √

3. Conduct research, gather data √

4. Evaluate hypotheses based on data

5. Cautiously draw conclusions
Next steps…gather data
 Once you have explicitly clear conceptual and
  operational definitions to guide the research, you must
  develop your measures for collecting data
   Operational definition proposes type of measures
 Instrumentation is the process of selecting or creating
  measures for a study (the measure is your instrument)
 Two overarching goals for instrumentation
   Validity: the extent to which a measure (operationally
     defined) taps the concept it’s designed to measure
     and not some other concept
   Reliability: the consistency or stability of a measure,
     i.e., same results obtained if measure used again
Caveats
 Can never be certain of the validity (or reliability) of our
  instruments so we try to speculate the degree of validity
   We might claim “modest” or “partial” validity
   Hard to capture true essence of a concept/construct and
       some concepts/constructs are more elusive than others!
 An estimate of the validity of our measures depends on the
  purpose of the study
   Keep focused on the hypotheses and operational definitions!
 Two types of validity we estimate
   Judgmental validity
   Empirical validity
  Types of validity: Judgmental
       Content validity: whether the concept being
        measured is a real concept AND whether the
        measurement being used is the most appropriate one
        to be using

             Is our operationally defined variable (concrete)
              really capturing the hypothetical concept (abstract)
Concept       we are interested in studying?

                Are we capturing the central meaning?
Variable/
Measure
Types of validity: Judgmental
 Content validity, or any other type of validity alone, is
  never enough to determine if our measure is valid so
  we consider other types…

 Face validity: measure is valid because it makes
  sense; on the surface, it seems to tap into construct of
  interest

    Face Validity is neither sufficient nor absolutely
     necessary for overall validity, but is a helpful clue
    Could have high face validity but low content
     validity!
Good face validity?
Rosenberg Self-Esteem Scale

1= Strongly Disagree, 7 = Strongly Agree

_____1. I feel that I am a person of worth, at least on an
   equal basis with others.
_____2. I feel that I have a number of good qualities.
_____3. All in all, I am inclined to think that I am a failure.*
_____4. I am able to do things as well as most people.
_____5. I feel that I do not have much to be proud of.*
_____6. I take a positive attitude towards myself.
_____7. On the whole, I am satisfied with myself.
_____8. I wish I could have more respect for myself.*
_____9. I certainly feel useless at times.*
_____10. At times I think I am no good at all.*

*Reverse scored
Types of validity: Empirical
•       Criterion-related Validity: extent to which your measure of a
        concept relates to a theoretically meaningful criterion for that
        concept, a “gold standard” for that concept
    •      Predictive validity: The measure should be able to predict future
           behavior that is related to the concept
          •   E.g., Job skills test and future ratings of performance
    •      Concurrent (convergent) validity: The measure should be
           meaningfully related or correlated to some other measure of the
           behavior
          •   E.g., Scores on two different job skills tests
    •      Predicitve or concurent validity coefficient: a number (0-1)
           based on correlation that quantifies whether the measure is in fact
           related to other measures it should be related to
Types of validity:
Judgmental-Empirical
 Construct validity represents a combined
  approach for estimating validity using
   1) a subjective prediction about what other
    concepts (indicators) the concept being
    measured should relate to and..
   2) an empirical test of whether the concept is
    in fact related to those other indicators
      E.g., Depression should be linked to
       disengagement from schoolwork among college
       students so test relationship between depression
       scores and GPA among a sample of students

				
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