Most frequently occurring number in the distribution o Least common measure of central tendency o Variability o Dispersion of numerical values o Range Subtract lowest score from highest score o Standard deviation Spread of scores around the mean o Correlation o The correlation of the coefficient reflects the degree of linear relationship between two variables o Range from -1.00 to +1.00 o Tell direction and magnitude o Direction Positive (+) Negative (-) o Magnitude Tells strength of the relationship o Regression
o Regression analysis is a statistical technique used to predict criterion performance based on predictor scores o Y=a+bX Y: predicted criterion score a: intercept b: slope X: predictor score for an individual Lecture 3 Reliability o Predictor: any variable used to forecast a criterion o Judge the goodness of a predictor with two psychometric criteria o Reliability Consistency, stability, or equivalence of a measure Four types Test-retest Equivalent form Internal consistency Inter-rater o Validity Test-retest o Reveals the stability of test scores upon repeated applications of the test o Generally, shorter time interval = higher test-rest reliability Equivalent forms reliability o Reveals the equivalence of test scores between two versions of the same test o Difficult to construct two measures with similar meanings and properties Internal consistency reliability o Reveals homogeneity of items comprising a test o Homogenous = item content is similar o Generally, the longer the test, the greater its reliability Inter-rater reliability o Reveals the degree of agreement among the assessments of two or more raters o Establishes whether behavior was reliably observed Reliability vs. Validity o Reliability = stability, consistency o Validity = accuracy, correctness o Accuracy or appropriateness of drawing inferences from test scores o Reliability is inherent in a measuring device; validity depends on the use of the test Construct validity o Construct = abstract, theoretical concept proposed to explain aspects of behavior o E.g. intelligence, leadership, motivation
o Construct validity = degree to which a test is an accurate measure of the construct it purports to measure o There should be evidence of o Convergent validity Scores on a test converge with scores on other known tests of the construct o Discriminant validity Scores on a test are unrelated to scores on tests of other constructs Criterion-related validity o Degree to which a test forecasts or is statistically related to a criterion o Validity coefficient = correlation of predictor scores with criterion scores o Desired range of validity coefficients is about 0.30-0.40
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