Item Response Theory
Item Response Theory (IRT) assumes that there is a correlation between the score gained by a candidate for one item/test (measurable) and their overall ability on the latent trait which underlies test performance (which we want to discover). Critically, the 'characteristics' of an item are said to be independent of the ability of the candidates who were sampled.

Item Response Theory comes in three forms: IRT1, IRT2, and IRT3 reflecting the number of parameters considered in each case.

IRT can be used to create a unique plot for each item (the Item Characteristic Curve - ICC). The ICC is a plot of Probability that the Item will be answered correctly against Ability. The shape of the ICC reflects the influence of the three factors:

This simple simulation allows the user to investigate the factors governing the shape of the Item Characteristic Curve. All three well known IRT models are represented (referred to as IRT1, IRT2 and IRT3) and Item Characteristic Curves can be super-imposed on one another to see how they relate.

content packageClick to download this Item Response Theory interface as an IMS Content Package: itemPIF.zip. The CP may be opened in Managed Learning Environment software such as WebCT or in the Reload Tools.
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