The description of Karen's test score stating that the true score lies within a 95% range (89–100) on any given day is an example of which psychometric concept?

• A. the standard error of measurement
• B. the mean score
• C. the standard deviation
• D. the percentile rank

Answer: (A)

The main idea here is measurement precision: a test score is not a perfectly exact reflection of a person’s true ability. The standard error of measurement (SEM) captures how much a single observed score is expected to differ from the true score because of measurement error. When we say the true score lies within a 95% range, we’re describing a confidence interval around the observed score that reflects this error—indicating where the actual ability would fall most of the time if the test were taken repeatedly.

This concept fits best because it directly links observed scores to an estimated true score and the precision of that estimate. A higher reliability (more consistent testing) yields a smaller SEM, narrowing the 95% range. The other options don’t describe this idea: the mean is just the average score, the standard deviation shows variability in a group, and percentile rank reflects relative position in a distribution rather than measurement precision for a single score.