摘要：The optimum number of alternatives in multiple choice items is studied. The new procedure applied is based on Item Response Theory and only needs a single sample. Concretely, a 5-alternative 221 items English Vocabulary test was administered to 452 people. Their answers to the 1/2/3 worst alternatives were randomly reassigned to generate their hypothetical answers to items of 4/3/2 alternatives, respectively. Changes in item parameters, test information function and ability estimation were analysed. The worst results were provided by 2-alternative items. As the results in the 3- and 4-alternative items do hardly differ from those obtained in the original 5-alternative case, and in the 3-alternative case the role of partial knowledge is less important, 3-alternative items were considered the best choice. The effects of number of alternatives on ability estimation was also discussed.
