02009nas a2200205 4500008004100000245008200041210006900123300001200192490000700204520132300211653002101534653001501555653003001570653001101600653000901611653004701620100001901667700001301686856010401699 2002 eng d00aHypergeometric family and item overlap rates in computerized adaptive testing0 aHypergeometric family and item overlap rates in computerized ada a387-3980 v673 aA computerized adaptive test (CAT) is usually administered to small groups of examinees at frequent time intervals. It is often the case that examinees who take the test earlier share information with examinees who will take the test later, thus increasing the risk that many items may become known. Item overlap rate for a group of examinees refers to the number of overlapping items encountered by these examinees divided by the test length. For a specific item pool, different item selection algorithms may yield different item overlap rates. An important issue in designing a good CAT item selection algorithm is to keep item overlap rate below a preset level. In doing so, it is important to investigate what the lowest rate could be for all possible item selection algorithms. In this paper we rigorously prove that if every item had an equal possibility to be selected from the pool in a fixed-length CAT, the number of overlapping item among any α randomly sampled examinees follows the hypergeometric distribution family for α ≥ 1. Thus, the expected values of the number of overlapping items among any randomly sampled α examinee can be calculated precisely. These values may serve as benchmarks in controlling item overlap rates for fixed-length adaptive tests. (PsycINFO Database Record (c) 2005 APA )10aAdaptive Testing10aAlgorithms10aComputer Assisted Testing10aTaking10aTest10aTime On Task computerized adaptive testing1 aChang, Hua-Hua1 aZhang, J uhttp://iacat.org/content/hypergeometric-family-and-item-overlap-rates-computerized-adaptive-testing