Item Analysis Platform Overview
Psychological measurement is the process of assigning quantitative values as representations of characteristics of individuals or objects, so-called psychological constructs. Measurement theories consist of the rules by which those quantitative values are assigned. Item Response Theory (IRT) is a measurement theory.
IRT uses a mathematical function to relate an individual’s probability of correctly responding to an item to a trait of that individual. Frequently, this trait is not directly measurable and is therefore called a latent trait.
To see how IRT relates traits to probabilities, first examine a test question that follows the Guttman “perfect scale” as shown in Figure 7.2
. The horizontal axis represents ...