Which statement best defines the true score in measurement?

• A. The observed score a student actually receives on a test.
• B. The score that would be obtained if measurement error were zero.
• C. The difference between observed score and error score.
• D. The sum of true score and observed score.

Answer: (B)

In measurement, the observed score reflects both the person’s actual level on the trait and some random error. The true score is that underlying level we would measure if there were no measurement error at all. That’s why the best statement is the one that describes the true score as what you would obtain if measurement error were zero. The observed score is what you actually get, and while conceptually true score could be seen as the observed score minus the error, the error is unknown in practice, so defining the true score as the zero-error value is the standard. The idea of adding true score and observed score would overcount, since the observed score already includes the true score plus error.