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NAEP Analysis and Scaling → Estimation of NAEP Score Scales → NAEP Assessment IRT Parameters

NAEP Assessment IRT Parameters


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Arts Assessment IRT Parameters
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Economics Assessment IRT Parameters
Geography Assessment IRT Parameters
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Reading Assessment IRT Parameters
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U.S. History Assessment IRT Parameters
Writing Assessment IRT Parameters

Mathematics Long-Term Trend Assessment IRT Parameters
Reading Long-Term Trend Assessment IRT Parameters

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During scaling, Item Response Theory (IRT) parameters are estimated using data from the current assessment and the most recent past assessment of the same subject if that past assessment was developed according to the same assessment framework. For items fitting the two-parameter IRT model, "a" and "b" parameters are estimated. For items fitting the three-parameter model, "a," "b," and "c" are estimated. For the generalized partial-credit model, "a," "b," and "d" parameters are estimated. There is an acceptable range of values for each IRT parameter. The "a" parameter ranges from 0 to 2. Generally, this value should never be negative. The "b" parameter varies from -3 to 3, and the "c" parameter varies from 0 to 1. The range of values for the "d" parameter is generally between -3 and 3, but can at times vary from -8 to 8. Items that are functioning poorly in a scale are identified early (i.e., during pilot studies and item analysis) and dropped from that scale. As with other IRT scaling procedures, person parameters are also estimated while the items are scaled; however, NAEP does not make use of these estimates, because group results based directly on these individual student parameters are inconsistent (Mislevy,1991). Note that the item parameters provided here are provided in the metrics used for the original calibration of the scales.

Last updated 15 December 2011 (GF)
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National Center for Education Statistics -
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