Abstract:

Item Parameter Drift (IPD) refers to change in parameter value (s) of the anchor item across several sequential testing occasions or test levels. This concept is essentially different from the concept of Differential Item Functioning (DIF). Current research on IPD spans five aspects: the practical existence, reasons, detection methods, and linking effects of IPD, and the strategy to the outlier anchor item. With respect to horizontal IPD, further and more comprehensive research is needed; esp., we should study the contextual applicability of DIF detection methods in the detection of IPD and develop detection methods for IPD specially, and develop revised linking procedures. Systematic and deep investigations are called up on vertical IPD.

Key words: test linking, parameter invariance, item parameter drift, differential item functioning, nonequivalent groups with anchor test design.