In item response theory, the item information function is a measure of how much statistical information a test item provides. Item information is a function of θ, the ability, proficiency, skill, or trait measured by the examinee’s responses to the test items. Figure 1 shows the information functions [Page 899]for four items. Items 1 and 2 are more informative at low values of θ than high values, and Items 3 and 4 are most informative at higher values of θ.
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