Baker, Frank B.2011-03-282011-03-281984Baker, Frank B. (1984). Ability metric transformations involved in vertical equating under item response theory. Applied Psychological Measurement, 8, 261-271. doi:10.1177/014662168400800302doi:10.1177/014662168400800302https://hdl.handle.net/11299/101910The metric transformations of the ability scales involved in three equating techniques-external anchor test, internal anchor test, and a pooled groups procedure -were investigated. Simulated item response data for two unique tests and a common test were obtained for two groups that differed with respect to mean ability and variability. The obtained metrics for various combinations of groups and tests were transformed to a common metric and then to the underlying ability metric. The results showed that there was reasonable agreement between the transformed obtained metrics and the underlying ability metric. They also showed that the largest errors in the ability score statistics occurred under the external anchor test procedure and the smallest under the pooled procedures. Although the pooled procedure performed well, it was affected by unequal variances in the two groups of examinees.enArticle