Within-Class Variability
Definition
The natural spread of measurements among items that share a common source, class, or category. For example, the range of refractive index values measured across different fragments from the same broken glass pane. Also called intra-class variability.
- Also called
- Intra-class variability
- Definition scope
- Spread among items sharing a common source or class
- Example domain
- Refractive index across fragments of one glass pane
Common questions
Why does within-class variability matter when comparing a questioned item to a known source?+
An examiner needs to know the natural spread of a measurement within a single known source before deciding whether a difference between questioned and known samples is meaningful or simply falls within the expected variation of that one source.
How does within-class variability differ from between-class variability?+
Within-class variability describes how much a property varies among items from the same source, while between-class variability describes how much that property differs across separate, unrelated sources; comparing the two is what lets an examiner judge whether a match is significant.
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...
- 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...
- Repeatability
- The agreement between successive measurements of the same specimen made by the same analyst, on the same instrument, in the same laboratory,...