| Abstract | Examinees working on competence tests frequently leave questions unanswered. As the missing values usually violate the missing at random condition, they pose a threat to drawing correct inferences about person abilities. In order to account appropriately for missing responses in the scaling of competence data, the mechanism resulting in missing responses needs to be modeled adequately. So far, studies have mainly focused on the evaluation of different approaches accounting for missing responses, making assumptions about the underlying missing mechanism. A deeper understanding of how and why missing responses occur can provide valuable information on the appropriateness of these assumptions. In the current study we investigate whether the missing tendency of a person depends on the competence domain assessed, or whether it can be considered a rather person-specific trait. Furthermore, we examine how missing responses relate to ability and other personality variables. We conduct our analyses separately for not-reached and omitted items, using data from the National Educational Panel Study (NEPS). Based on an IRT approach by Holman and Glas (2005), we investigate the missing process in the competence domains information and communication technologies, science, mathematics, and reading, which were assessed in three age cohorts (fifth-graders: N= 5,193, ninth-graders: N= 15,396, adults: = 7,256). Results demonstrate that persons’ missing propensities may, to some extent, be regarded as person-specific. The occurrence of omissions and not-reached items mainly depends on persons’ competencies, and is different for people with a migration background and for students attending different school types, even after controlling for competencies. Our findings should be considered in approaches aiming at accounting for missing responses in the scaling competence data. (Orig.). |
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