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Ch. 5

Ch. 5. Measurement Concepts. Reliability of measures. Reliability 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

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Ch. 5

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  1. Ch. 5 Measurement Concepts

  2. Reliability of measures • Reliability • 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 0.00-1.00 and 0.00- (-)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 __________________________________________ • Reactivity of measures • Potential problem when measuring behavior • AWARENESS OF BEING MEASURED CHANGES AN INDIVIDUAL’S BEHAVIOR

  6. Construct validity of measures • Construct validity • 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 orientedvalidity: the relationship between scores on the measure and some criterion

  7. Construct validity of measures • Construct validity • 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 • Construct validity • 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

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