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The Stability of Equated Test Scores (Revised Edition)

Karon, Bertram P.
Publication Year:
Report Number:
ETS Research Bulletin
Document Type:
Page Count:
Subject/Key Words:
Anchor Tests, Equated Scores, Sampling, Statistical Bias, Test Reliability


The effects of sampling error were studied empirically with respect to four methods of equating scales of tests administered to non-overlapping groups of subjects: (1) mean and sigma method, (2) equi-percentile method, (3) maximum likelihood method using an "anchor" test, (4) standard reference group method using an "anchor" test. The methods were compared under both random and stratified sampling. Results showed that sampling error was (1) smaller for those methods which make use of an "anchor" test than for those which do not, (2) smaller for equated scores closer to the mean of the total population than for those further from the mean, (3) was not decreased by stratification by institution when the "anchor" test methods of equating were used.

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