Repeatability
Definition
The agreement between successive measurements of the same specimen made by the same analyst, on the same instrument, in the same laboratory, within a short time. Sets the minimum floor of variability for a method. Reproducibility extends this to changed conditions such as different analysts or laboratories.
- Conditions
- Same analyst, instrument, lab, short timeframe
- Measures
- Minimum floor of method variability
- Related term
- Reproducibility, tested under changed conditions
- Sub-field
- Method validation, quality assurance
Common questions
Why does a lab need repeatability data before it needs reproducibility data?+
Repeatability establishes the best-case variability a method can achieve under fixed conditions, and if that floor is already too high, changing analysts or laboratories in a reproducibility study will only add further variability, so repeatability is assessed first.
How is repeatability typically expressed in a validation report?+
It is usually reported as a standard deviation or coefficient of variation across repeated measurements of the same specimen, giving a numeric baseline the lab compares against its stated method tolerances.
Does poor repeatability necessarily mean the analyst made an error?+
Not necessarily, poor repeatability can also reflect instrument drift, sample heterogeneity, or a method that is inherently more variable near certain concentration ranges, so it prompts investigation rather than an automatic assumption of analyst mistake.
Related terms
- Accuracy
- The degree to which a measured value agrees with the accepted true or reference value of the quantity. A biased instrument can...
- Between-Class Variability
- The spread of measurements between items from different sources or categories. A forensic method is most discriminating when between-class variability is large...
- Limit of Detection (LOD)
- The lowest concentration of analyte that produces a signal reliably distinguishable from the instrument noise, conventionally three times the standard deviation of...
- Limit of Quantitation (LOQ)
- The lowest concentration at which the assay can produce a quantitative measurement with acceptable precision and accuracy, typically defined as the concentration...
- Measurement Error
- The discrepancy between a recorded value and the true value of the property being measured. Arises from instrument calibration limits, analyst technique,...
- Precision
- The degree to which repeated measurements of the same specimen under the same conditions agree with each other. Quantified by the standard...
- Reproducibility
- The closeness of agreement between measurements obtained under changed conditions: different analysts, different instruments, different laboratories, or different times. A wider measure...
- Robustness
- The capacity of a method to remain unaffected by small, deliberate variations in its operating parameters, such as slight changes in temperature,...
- Selectivity
- The ability of a method to measure the target analyte specifically, even when other substances that might plausibly appear in a real...
- Within-Class Variability
- The natural spread of measurements among items that share a common source, class, or category. For example, the range of refractive index...
Explained in these topics
- Method Validation and Fitness for PurposeThe closeness of agreement between repeated measurements of the same sample by the same analyst on the same instrument under identical conditions over a short...
- Variability and Measurement Error