2: Item Analysis

This chapter introduces statistical procedures to conduct item analyses based on classical test theory (CTT). These analyses will typically serve as a first step in the investigation of the psychometric properties of scale scores. Analyses described in this chapter provide ways to estimate the difficulty and discrimination of dichotomously (e.g., correct/incorrect) and polytomously (e.g., disagree, neutral, agree) scored questionnaire and test items. Understanding the characteristics of scale items is a necessary step for deciding which items will remain, be revised, or be excluded from the final version of a psychological or educational measure (e.g., motivation, mathematics achievement). Additionally, the steps for developing an automatic scoring routine for a survey or test are provided at the end of the chapter.