In the Item Analysis report, the Parameter Estimates section contains a table of estimated parameters for each item. The parameters provided depend on the model used in your analysis (1PL, 2PL, or 3PL).
Item
The test item.
Difficulty
The b parameter or the measure of the difficulty of the item. A histogram of the difficulty parameters is shown beside the difficulty estimates.
Discrimination
(Available only for 2PL and 3PL models.) The a parameter or the measure of the item discrimination. A histogram of the discrimination parameters is shown beside the discrimination estimates.
Lower Asymptote
(Available only for 3PL models.) The c parameter or a measure of guessing.