Item Difficulty and Discrimination as a Function of Stem Completeness

Abstract

The effects on item difficulty and discrimination of stem completeness (complete stem or incomplete stem) for multiple-choice items were studied experimentally. Subjects (166 junior education students) were classified into three achievement groups (low, medium, high) and one of two forms of a multiple-choice test was randomly assigned to each subject. A two-way factorial design (completeness × achievement) was used as the experimental model. Analysis indicated that stem completeness had no effect on either item discrimination or difficulty and there was no interaction effect with achievement. It was concluded that multiple-choice items may be very robust in measuring knowledge in a subject area irrespective of variations in stem construction.