EDMS 623 Chapter 5 notes - Chapter 5: Test Scores as...

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Chapter 5: Test Scores as Composites Test battery: collection of two or more separate tests designed to be administered to the same examinees. Separate score is computed for each test. o Example: GRE separate score for verbal, quantitative, and analytic. Composite test score : total score created by summing two or more subtest scores. Item score : number of points assigned to an individual’s response to a given item. Total score: usually determined by summing the item scores. Every test score is a composite. Scoring for most items can be classified as either dichotomous or nondichotomous. Variability of responses displayed by the group for an item: calculate the variance of that set of item responses. Item difficulty: (p) the proportion of examinees who answer an item correctly. o P of 0.85: an item answered correctly by 85% of the examinees. o Thus, the easier item actually has the higher item difficulty value. Dichotomous variables: when all values are restricted to 0 or 1, the mean of item will be equivalent to the number of persons with a score of 1 on item (pj = mean j) When items are dichotomous, variance formula pjqj , where qj = 1- pj Total test score variance > sum of item variances o Total test variance is not determined by individual item variances. For any pair of variables taken on the same sample, covariance the correlation of those two variables multiplied by their standard deviations. There will always be one variance term for each item and a pair of covariance terms for each pair of items (2pjSiSj) Total variance of a composite : determined jointly by the variance of individual test items and by the covariance of all pairs of those items. Composite variance for a test with n items will have n variance terms and n(n -1) covariance terms. However, there are only n(n-1)/2 UNIQUE covariance terms. Variance: individual differences
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EDMS 623 Chapter 5 notes - Chapter 5: Test Scores as...

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