tion with (Huber ability estimate) polytomous items is still experimental!</p>
    <h2 class="hasAnchor" id="references"><a class="anchor" href="#references"></a>References</h2>

    <p>Baker, Frank B., and Kim, Seock-Ho (2004). Item Response Theory - Parameter Estimation Techniques. CRC-Press.</p>
<p>Barton, M. A., &amp; Lord, F. M. (1981). An Upper Asymptote for the Three-Parameter Logistic Item-Response Model.</p>
<p>Magis, D. (2013). A note on the item information function of the four-parameter logistic