Response time-based treatment of omitted responses in computer-based testing

Abstract

A new response time-based method for coding omitted item responses in computer-based testing is introduced and illustrated with empirical data. The new method is derived from the theory of missing data problems of Rubin and colleagues and embedded in an item response theory framework. Its basic idea is using item response times to statistically test for each individual item whether omitted responses are missing completely at random (MCAR) or missing due to a lack of ability and, thus, not at random (MNAR) with fixed type-1 and type-2 error levels. If the MCAR hypothesis is maintained, omitted responses are coded as not administered (NA), and as incorrect (0) otherwise. The empirical illustration draws from the responses given by N = 766 students to 70 items of a computer-based ICT skills test. The new method is compared with the two common deterministic methods of scoring omitted responses as 0 or as NA. In result, response time thresholds from 18 to 58 s were identified. With 61%, more omitted responses were recoded into 0 than into NA (39%). The differences in difficulty were larger when the new method was compared to deterministically scoring omitted responses as NA compared to scoring omitted responses as 0. The variances and reliabilities obtained under the three methods showed small differences. The paper concludes with a discussion of the practical relevance of the observed effect sizes, and with recommendations for the practical use of the new method as a method to be applied in the early stage of data processing.