Which is the best indicator of precision in a laboratory measurement?

• A. Standard deviation
• B. Coefficient of variation
• C. Mean
• D. Range

Answer: (B)

Precision is about how tightly repeated measurements cluster around the same value. The coefficient of variation is the best indicator because it puts the variability in relation to the average magnitude of the measurement, making comparisons across different tests meaningful. It’s calculated as (standard deviation / mean) × 100 and is unitless, so you can compare precision between different analytes, instruments, or methods. A smaller coefficient of variation means higher precision.

Standard deviation shows how spread out the data are, but since it has the same units as the measurement, it’s not directly comparable when means differ. The mean only tells you the central value, not how variable the results are, and the range depends on extreme values and sample size, offering a crude, sometimes misleading sense of spread.