In this paper, a new item analysis index, e, is derived as a function of difficulty and discrimination to represent item efficiency. Item discrimination in this paper is not independent of item difficulty, and it is demonstrated algebraically that the maximum discriminating power of an item may be determined from its difficulty. Item efficiency is defined as the ratio of observed discrimination to maximum discrimination. The e-index will range from zero to unity and will provide additional information for item analyses. Its probability interpretations may provide an attractive psychometric criterion for the retention or rejection of items. (Author)