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ERIC Number: EJ1092629
Record Type: Journal
Publication Date: 2016-Apr
Pages: 22
Abstractor: As Provided
Reference Count: 26
ISBN: N/A
ISSN: ISSN-0013-1644
Unidimensional IRT Item Parameter Estimates across Equivalent Test Forms with Confounding Specifications within Dimensions
Matlock, Ki Lynn; Turner, Ronna
Educational and Psychological Measurement, v76 n2 p258-279 Apr 2016
When constructing multiple test forms, the number of items and the total test difficulty are often equivalent. Not all test developers match the number of items and/or average item difficulty within subcontent areas. In this simulation study, six test forms were constructed having an equal number of items and average item difficulty overall. Manipulated variables were the number of items and average item difficulty within subsets of items primarily measuring one of two dimensions. Data sets were simulated at four levels of correlation (0, 0.3, 0.6, and 0.9). Item parameters were estimated using the Rasch and two-parameter logistic unidimensional item response theory models. Estimated discrimination and difficulty were compared across forms and to the true item parameters. The average unidimensional estimated discrimination was consistent across forms having the same correlation. Forms having a larger set of easy items measuring one dimension were estimated as being more difficult than forms having a larger set of hard items. Estimates were also investigated within subsets of items, and measures of bias were reported. This study encourages test developers to not only maintain consistent test specifications across forms as a whole but also within subcontent areas.
SAGE Publications. 2455 Teller Road, Thousand Oaks, CA 91320. Tel: 800-818-7243; Tel: 805-499-9774; Fax: 800-583-2665; e-mail: journals@sagepub.com; Web site: http://sagepub.com
Publication Type: Journal Articles; Reports - Research
Education Level: N/A
Audience: N/A
Language: English
Sponsor: N/A
Authoring Institution: N/A