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Lecture 4

PSYB01 - Lecture 4 Notes

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University of Toronto Scarborough
Anna Nagy

Research Methods September 26th, 2013 - Lecture 4 Measurement Concepts Learning Objectives  Define reliability of a measure of behavior and describe the difference between test-retest, internal consistency, and interrater reliability.  Discuss ways to establish construct validity, including predictive validity, concurrent validity, convergent validity, and discriminant validity.  Describe the problem of reactivity of a measure of behavior and discuss ways to minimize reactivity.  Describe the properties of the four scales of measurement: nominal, ordinal, interval, and ratio. Reliability of Measures  Consistency or Stability of a Measure of Behavior  True Score  Measurement Error  Pearson Product-Moment Correlation Coefficient True Score Theory of Reliability Reliability  Proportion of true scores in a measure  But characteristic of a measure taken across individuals  Look at variance in scores across subjects Variance of true scores (T) ____________________ Variance of the measure (X)  Don’t know true scores, so can’t calculate reliability of true scores…must estimate  Assume measured scores (X) related to each other to the degree that they share true scores  Estimate of reliability=correlation between two scores of the same measure How to Estimate Reliability--Pearson r  Correlation coefficients called regression coefficients (reliability coeffiecient) used for ratio and interval scales  Coefficients range from 0.00 to - 1.00 and 0.00 to +1.00 Estimating Reliability Estimation of Reliability  Will always range between 0 & 1. Examples:  Reliability of .6 means that approx. 60% of scores attributable to true score and 40% to error  Reliability of .75 means that approx. 75% of scores attributable to true score and 25% to error… Internal Consistency Reliability  Test-Retest Reliability  Assessed by measuring the same individuals two points in time (subjects position in relative distribution of scores should be similar)  Assumes no substantial change in construct or condition over time  Vulnerable to artificiality  Vulnerable to maturation  Parallel forms - challenging  Use single measurement on one occasion to determine an estimate of reliability  Administered to a large group of people Reliability Estimates  Internal Consistency Reliability  Inter-Item Correlations  Internal Consistency Reliability  Inter-total Correlations  Split-half reliability  Cronbach’s alpha  Equal to the average of all split half correlations  items that do not correlate with other items can be eliminated from the measure to increase reliability Reliability of Measures Interrater Reliability - Correlation between the observations of raters Inter-rater Reliability How to Calculate Interrater Reliability--Percentage agreement Example: Inter-observer or Interrater Reliability Number of times two observers agree _______________________________ x100 Number of opportunities to agree How to Calculate Interrater Reliability—Correlations between raters • Calibrate the observers for continuous measures • Rating of overall noise level in classroom on a scale of 1 to 10 • Have raters provide ratings every five minutes • Correlation between overall ratings would give estimate of reliability between raters Research and Critical Thinking: Assessing the impact of parent and teacher agreement on diagnosing atten
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