Analysis of the optimum number alternatives from the Item Response Theory

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 si ngle sample. Concretely, a 5-alternative 221 items English Vocabulary test was administered to 452 people. Their answers to the 1/2/3 worst alternativ es were randomly reassigned to generate their hypothetical answers to items of 4/3/2 alternatives, respectively. Changes in item parameters, test info rmation function and ability estimation were analysed. The worst results we re provided by 2-alternative items. As the results in the 3- and 4-alternat ive items do hardly differ from those obtained in the original 5-alternativ e case, and in the 3-alternative case the role of partial knowledge is less important, 3-alternative items were considered the best choice. The effect s of number of alternatives on ability estimation was also discussed.