Accuracy and precision
From The Art and Popular Culture Encyclopedia
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In the fields of science, engineering, industry and statistics, the accuracy of a measurement system, also called reproducibility or repeatability, is the degree to which repeated measurements under unchanged conditions show the same results. Although the two words reproducibility and repeatability can be synonymous in colloquial use, they are deliberately contrasted in the context of the scientific method.
A measurement system can be accurate but not precise, precise but not accurate, neither, or both. For example, if an experiment contains a systematic error, then increasing the sample size generally increases precision but does not improve accuracy. The result would be a consistent yet inaccurate string of results from the flawed experiment. Eliminating the systematic error improves accuracy but does not change precision.
A measurement system is designated valid if it is both accurate and precise. Related terms include bias (non-random or directed effects caused by a factor or factors unrelated to the independent variable) and error (random variability).
The terminology is also applied to indirect measurements—that is, values obtained by a computational procedure from observed data.
In addition to accuracy and precision, measurements may also have a measurement resolution, which is the smallest change in the underlying physical quantity that produces a response in the measurement.
In the case of full reproducibility, such as when rounding a number to a representable floating point number, the word precision has a meaning not related to reproducibility. For example, in the IEEE 754-2008 standard it means the number of bits in the significand, so it is used as a measure for the relative accuracy with which an arbitrary number can be represented.
See also
- ± or Plus-minus sign
- Accuracy class
- ANOVA Gauge R&R
- ASTM E177 Standard Practice for Use of the Terms Precision and Bias in ASTM Test Methods
- Engineering tolerance
- Experimental uncertainty analysis
- Failure assessment
- Precision bias
- Precision engineering
- Precision (statistics)
- Accepted and experimental value
- Binary classification
- Brier score
- Confusion matrix
- Detection theory
- F-score
- Gain (information retrieval)
- Matthews correlation coefficient
- Precision and recall curves
- Receiver operating characteristic or ROC curve
- Sensitivity and specificity
- Selectivity
- Sensitivity index
- Statistical significance
- Youden's J statistic