Treating Noneffortful Responses as Missing.

This study investigates the treatment of rapid-guess (RG) responses as missing data within the context of the effort-moderated model. Through a series of illustrations, this study demonstrates that the effort-moderated model assumes missing at random (MAR) rather than missing completely at random (MCAR), explaining the conditions necessary for MAR. These examples show that RG responses, when treated as missing under the effort-moderated model, do not introduce bias into ability estimates if the missingness mechanism is properly accounted for. Conversely, using a standard item response theory (IRT) model (scoring RG responses as if they were valid) instead of the effort-moderated model leads to considerable biases, underestimating group means and overestimating standard deviations when the item parameters are known, or overestimating item difficulty if the item parameters are estimated.