Measurement quality terms: Which term specifically describes the repeatability (closeness of agreement among repeated measurements) of a measurement process?

Introduction / Context:
In test and measurement, two often-confused qualities are accuracy and precision. Precision addresses how tightly repeated measurements cluster, whereas accuracy addresses how close a measurement is to the true value. Distinguishing the two guides calibration, instrument selection, and uncertainty reporting.

Given Data / Assumptions:

• We consider repeated measurements of the same measurand under similar conditions.
• Random and systematic errors may both be present.
• Terminology follows common metrology usage.

Concept / Approach:

Precision is high when the spread (standard deviation) of repeated measurements is small. Accuracy is high when the average value is close to the true value (low bias). An instrument can be precise but inaccurate (tight cluster, shifted from truth) or accurate but imprecise (average near truth but widely scattered). Error is the deviation; bias is the systematic component of error.

Step-by-Step Solution:

Verification / Alternative check:

Plot measurement runs on a histogram or target chart: a tight cluster (narrow distribution) indicates high precision. A cluster centered on the true value indicates high accuracy. These visual checks reinforce the definitions used in quality systems (e.g., ISO 5725 concepts).

Why Other Options Are Wrong:

• error: A general deviation measure, not specifically repeatability.
• accuracy: Refers to closeness to true value, not clustering of repeats.
• significant: Not a measurement quality term on its own.
• bias: Systematic error component, not overall repeatability.

Common Pitfalls:

• Equating a tight cluster (precision) with correctness (accuracy).
• Ignoring environmental factors that increase scatter and reduce precision.

Final Answer:

precision