Reliability and Item Analysis Introductory Overview - Classical Testing Model

To summarize the concepts discussed in Basic Ideas, each measurement (response to an item) reflects to some extent the true score for the intended concept (prejudice against foreign cars), and to some extent esoteric, random error. We can express this in an equation as:

X = Tau + error

In this equation, X refers to the respective actual measurement, that is, subject's response to a particular item; Tau is commonly used to refer to the true score, and error refers to the random error component in the measurement.