1. Ch. 5
Measurement Concepts

2. Reliability of measures
Reliability is a necessary but not sufficient condition for validity.
The consistency or stability of a measure of behavior
Measure (Observed score) = true score + measurement error
Unreliable measures have large margins of measurement error
Assessment of stability of measures is done using correlation coefficients
Pearson product-moment correlation coefficient
Ranges from and (-)1.00
If r is + there is a + relationship and vice versa

3. Reliability of measures
Test-Retest Reliability
Measuring the same individuals at 2 points in time to get similar results
Similar results reflect true scores rather than measurement error
Reliability coefficients should be at least 0.80
Drawback -

4. Reliability of measures
Internal consistency reliability
Devised to control for error in test-retest experiments
Assessment of reliability using responses at only 1 time point
This form of reliability is dependent on how well the items on the test measure what they are supposed to
Split half reliability
Using ½ of the scores to compare to the other ½
Or using odd #s to compare to even #s

5. Reliability of measures
Interrater reliability
The extent to which raters agree in their observations
High reliability = Similar observations
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Reactivity of measures
Potential problem when measuring behavior
AWARENESS OF BEING MEASURED CHANGES AN INDIVIDUAL’S BEHAVIOR

6. Construct validity of measures
The adequacy of the operational definition of variables; The measure has construct validity if it measures what it is supposed to
Indicators of construct validity
Face validity: the measure appears to measure what it’s supposed to
Criterion oriented validity: the relationship between scores on the measure and some criterion

7. Construct validity of measures
Criterion oriented validity
Predictive validity:
the extent to which the measure allows you to predict behaviors that it should predict
i.e. GRE developed to predict behavior in a graduate program
Concurrent validity:
whether 2 or more groups of people differ on the measure in expected ways
a measure that allows a researcher to distinguish between people at the present time

8. Construct validity of measures
Criterion oriented validity
Convergent validity:
the extent to which scores on the measure in question are related to scores on other measures of the same construct or similar constructs
showing that measures that should be related, in reality are related
Discriminant validity:
demonstrated when the measure is not related to variables with which it should not be related
Showing that measures that are NOT related, in reality are NOT related

9. Variables and measurement scales
Nominal scales
Ordinal scales
Interval scales
Ratio scales

10. Importance of measurement scales
The scale used determines the amount of information provided by a particular measure
Interval and ratio scales allow the researcher to make quantitative assumptions