Abstract
Several person-fit statistics have been proposed to detect item score patterns that do not fit an item response theory model. To classify response patterns as misfitting, the distribution of a person-fit statistic is needed. The theoretical null distributions of several fit statistics have been derived for paper-and-pencil (P&P) tests. However, it is unknown whether these distributions also hold for computerized adaptive tests (CAT). A three-part simulation study was conducted. In the first study, the theoretical distribution of the l z statistic across trait. θlevels for CAT and P&P tests was investigated. The distribution of the l* z statistic proposed by Snijders (in press) was also investigated. Results indicated that the distribution of both l z and l* z differed from the theoretical distribution in CAT. The second study examined the distributions of l z and l* z using simulation. These simulated distributions, when based on O [UNKNOWN], were found to be problematic in CAT. In the third study, the detection rates of l* z and l z were compared. The rates for both statistics were found to be similar in most cases.
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