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Modeling and Multivariate Methods - SAS

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532 Scoring Tests Using Item Response Theory Chapter 22<br />

Item Analysis Output<br />

Figure 22.11 Dual Plot<br />

Questions are plotted to the left of the vertical dotted line, examinees on the right. In addition, a histogram<br />

of ability levels is appended to the right side of the plot.<br />

This example shows a wide range of abilities. Q10 is rated as difficult, with an examinee needing to be<br />

around half a st<strong>and</strong>ard deviation above the mean in order to have a 50% chance of correctly answering the<br />

question. Other questions are distributed at lower ability levels, with Q11 <strong>and</strong> Q4 appearing as easier. There<br />

are some questions that are off the displayed scale (Q7 <strong>and</strong> Q14).<br />

The estimated parameter estimates appear below the Dual Plot, as shown in Figure 22.12.

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