Introduction to Measurement

1
Introduction to Measurement

• Construct the characteristic or aspect of the
  person that the psychologist would like to
  measure.
• Test Construction The operational definition of
  a construct.
• Validity Does the test measure what its
  supposed to measure?
• Reliability Is the test consistent? Can we count
  on the scores from the test?

2

• True-Score Theory
• True Score Place on the scale of possible scores
  where the person really is.
• X True score
• X True Score Error

3
Where does the error come from?

• Test Construction
• Domain of Sampling the full set of information
  to assess a construct.
• The measure may
• Obtain information from a different construct
• Not obtain all the information relevant to a
  construct.

4
Errors in Test Construction Contd

• 2. Test Administration
• 1. Differences in testing materials
• 2. Differences in testing conditions
• 3. Differences about the examiner
• 3. Test Scoring and Interpretation

5
Reliability

• Reliability refers to the consistency of the
  testing instrument.
• Test-retest reliability
• 2. Internal consistency All the items are
  measuring the same construct.
• Split-half reliability
• Cronbachs Alpha (Coefficient Alpha) average
  correlation among the items.
• .8 is a good number to aim for.

6
Correlation Matrix

• Average correlation .75
• 
  1 2 3
  4
• 1. Dedicate my life to Stats 1.0
  -.75 .84 -.65
• 2. I hate stats
  1.0 -.92 .73
• 3. I enjoy my statistics courses
  1.0 -.62
• 4. I would rather break my leg
  1.0

7
Validity

• Validity the test measures what it is supposed
  to measure.
• Construct Validity The test measures the
  construct it is supposed to measure
• Convergent Validity the test is strongly
  correlated with other measures of the same
  construct
• Discriminant Validity The test is not strongly
  correlated with tests measuring different
  constructs

8
Correlation Matrix Assessing Construct Validity

• 
  1 2 3
  
• 1. Pierce Depression Scale 1.0
  .65 -.04
• 2. Beck Depression Inventory
  1.0 .07
• 3. I Like Dirt Scale
  1.0

9
Correlation Matrix

• Convergent
  Validity Discriminant Validity
• 
  1 2 3
  
• 1. Pierce Depression Scale 1.0
  .65 -.04
• 2. Beck Depression Inventory
  1.0 .07
• 3. I Like Dirt Scale
  1.0

10
(No Transcript)