Accuracy And Precision
In the fields of science, engineering, industry and statistics, the accuracy of a measurement system is the degree of closeness of measurements of a quantity to that quantity's actual (true) value. The precision 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.
Read more about Accuracy And Precision: Accuracy Versus Precision: The Target Analogy, Quantification, In Binary Classification, In Psychometrics and Psychophysics, In Logic Simulation, In Information Systems
Famous quotes containing the words accuracy and/or precision:
“As for farming, I am convinced that my genius dates from an older era than the agricultural. I would at least strike my spade into the earth with such careless freedom but accuracy as the woodpecker his bill into a tree.”
—Henry David Thoreau (1817–1862)
“Some authorities hold that the young ought not to lie at all. That, of course, is putting it rather stronger than necessary; still, while I cannot go quite so far as that, I do maintain, and I believe I am right, that the young ought to be temperate in the use of this great art until practice and experience shall give them that confidence, elegance and precision which alone can make the accomplishment graceful and profitable.”
—Mark Twain [Samuel Langhorne Clemens] (1835–1910)