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Chapter 4

Psychological Assessment - Chapter 4 Book Notes

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Reliability Discrepancies between the true ability and measurement of ability form errors of measurement Error means that there will always be some inaccuracy in our measurements Tests that are relatively free of measurement error are said to be reliable History and Theory of Reliability Spearmans Early Studies Charles Spearman is responsible for the advanced development of reliability assessment Moivre introduced the basis notion of sampling error Pearson development the product moment correlation Spearman worked out most of the basics of contemporary reliability theory Spearmans article attracted Thorndike Item response theory (IRT): uses computer technology to advance psychological measurement significantly IRT is built on many of the ideas that Spearman introduced Basics of Test Score Theory The observed score for each person always differs from the persons true ability The difference is the measurement error A major assumption of the classical test theory is that errors of measurement are random Basic sampling theory: tells us that the distribution of random errors is bell-shaped The center of the distribution represents the true show www.notesolution.com The dispersion about the mean of the distributions display the distribution of sampling errors The true score for an individual will not change with repeated applications of the same test Standard deviation = standard error of measurement The standard error of measurement tell us, on average, how much a score varies from the true score The standard deviation of the observed scored and the reliability of the test are used to estimate the standard error of measurement The Domain Sampling Model Domain sampling model: considers the problem created by using a limited number of items to represent a larger and more complicated constract The error is due to the sample of items As the sample gets larger, it represents the domain more and more accurately The greater the number of items, the higher the reliability Each item on the test should represent the studied ability Reliability can be estimated from the correlation of the observed test score with the true score, but true scores are not available Our only alternative is to estimate that the true score is Different random samples of items might give different estimates of the true score due to sampling error To estimate reliability, we create many randomly parallel tests by drawing repeated random samples of items from the same domain If we create many tests from sampling, we should get a normal distribution of unbiased estimates of the true score Then we would find the correlation between each tests and each of other tests, and the correlations then would be averaged Item Response Theory www.notesolution.com
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