If the standard error of measurement increases, what happens to the width of the confidence interval around an observed score?

• A. It increases
• B. It decreases
• C. It remains the same
• D. It becomes zero

Answer: (A)

A larger standard error of measurement means more measurement error and less precision, so the confidence interval around an observed score widens. The margin of error that defines the interval is proportional to the SEM (often margin ≈ z times SEM, with the width being twice that margin). So when SEM increases, the interval grows wider to reflect greater uncertainty about the true score. The observed score itself doesn’t change, and the level of confidence is unchanged; it’s the uncertainty surrounding the true score that increases, not a fixed center.