Item Parameter Drift: concepts, methodology and identifying

Item Parameter Drift occurs over time for various reasons; when test items lose their initial characteristics, such as difficulty and discrimination parameters. Including cases of item parameter drift are revealed, excessive repetition, changes in the education system, and the position of items and the parameters of poor initialization. Item parameter drift causes of the invariance to be violated. There are two types of uniform (change of discrimination parameter) and non-uniformity (change of difficulty parameter) drift. Conceptually and methodologically, this concept is parallel to the concept of differential functioning, with the difference that instead of group differences the periods are examined. In order to after observing the undimensionality, with a little change, the recognition of differential item functioning methods is used. After identifying the drift, it must be determined whether changes in the content, motivation conditions, response time and place of the item are compared with when the item was created. If any of these conditions exist, the item must be removed from the set of items or be reset to the parameter.