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==Date: 1740==
*1 : the [[quality]] or state of being precise : exactness
*2 a : the [[degree]] of refinement with which an operation is [[performed]] or a measurement stated — compare accuracy
:b : the accuracy (as in binary or [[decimal]] places) with which a number can be [[represented]] usually [[expressed]] in terms of the number of computer words available for representation <double precision arithmetic permits the representation of an expression by two computer words>
==Description==
The '''accuracy''' of a measurement [[system]] is the [[degree]] of closeness of [[measurements]] of a [[quantity]] to its [[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]] can be synonymous in colloquial use, they are deliberately [[contrasted]] in the [[context]] of the [[scientific method]].
Accuracy indicates proximity of measurement results to the true [[value]], precision to the repeatability or reproducibility of the measurement.
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. Eliminating the systematic error improves accuracy but does not change precision.
A measurement system is called valid if it is both accurate and precise. Related terms are bias (non-random or directed [[effects]] caused by a [[factor]] or factors unrelated by the [[independent]] [[variable]]) and error (random variability), respectively.
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 have also a measurement resolution, which is the smallest [[change]] in the underlying [[physical]] [[quantity]] that produces a [[response]] in the measurement. Its precision, however, may be low.
==Target Analogy==
Accuracy is the degree of veracity while precision is the degree of reproducibility. The [[analogy]] used here to explain the [[difference]] between accuracy and precision is the target [[comparison]]. In this analogy, repeated measurements are compared to arrows that are shot at a target. Accuracy describes the closeness of arrows to the bullseye at the target [[center]]. Arrows that strike closer to the bullseye are considered more accurate. The closer a system's measurements to the accepted [[value]], the more accurate the system is considered to be.
To continue the analogy, if a large [[number]] of arrows are shot, precision would be the size of the arrow cluster. (When only one arrow is shot, precision is the size of the cluster one would expect if this were repeated many times under the same conditions.) When all arrows are grouped tightly [[together]], the cluster is considered precise since they all struck close to the same spot, even if not necessarily near the bullseye. The measurements are precise, though not necessarily accurate.
However, it is not possible to reliably [[achieve]] accuracy in [[individual]] measurements without precision—if the arrows are not grouped close to one another, they cannot all be close to the bullseye. (Their [[average]] position might be an accurate estimation of the bullseye, but the [[individual]] arrows are inaccurate.) See also circular error probable for application of precision to the [[science]] of [http://en.wikipedia.org/wiki/Ballistics ballistics].[http://en.wikipedia.org/wiki/Accuracy_and_precision]
[[Category: General Reference]]
==Date: 1740==
*1 : the [[quality]] or state of being precise : exactness
*2 a : the [[degree]] of refinement with which an operation is [[performed]] or a measurement stated — compare accuracy
:b : the accuracy (as in binary or [[decimal]] places) with which a number can be [[represented]] usually [[expressed]] in terms of the number of computer words available for representation <double precision arithmetic permits the representation of an expression by two computer words>
==Description==
The '''accuracy''' of a measurement [[system]] is the [[degree]] of closeness of [[measurements]] of a [[quantity]] to its [[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]] can be synonymous in colloquial use, they are deliberately [[contrasted]] in the [[context]] of the [[scientific method]].
Accuracy indicates proximity of measurement results to the true [[value]], precision to the repeatability or reproducibility of the measurement.
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. Eliminating the systematic error improves accuracy but does not change precision.
A measurement system is called valid if it is both accurate and precise. Related terms are bias (non-random or directed [[effects]] caused by a [[factor]] or factors unrelated by the [[independent]] [[variable]]) and error (random variability), respectively.
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 have also a measurement resolution, which is the smallest [[change]] in the underlying [[physical]] [[quantity]] that produces a [[response]] in the measurement. Its precision, however, may be low.
==Target Analogy==
Accuracy is the degree of veracity while precision is the degree of reproducibility. The [[analogy]] used here to explain the [[difference]] between accuracy and precision is the target [[comparison]]. In this analogy, repeated measurements are compared to arrows that are shot at a target. Accuracy describes the closeness of arrows to the bullseye at the target [[center]]. Arrows that strike closer to the bullseye are considered more accurate. The closer a system's measurements to the accepted [[value]], the more accurate the system is considered to be.
To continue the analogy, if a large [[number]] of arrows are shot, precision would be the size of the arrow cluster. (When only one arrow is shot, precision is the size of the cluster one would expect if this were repeated many times under the same conditions.) When all arrows are grouped tightly [[together]], the cluster is considered precise since they all struck close to the same spot, even if not necessarily near the bullseye. The measurements are precise, though not necessarily accurate.
However, it is not possible to reliably [[achieve]] accuracy in [[individual]] measurements without precision—if the arrows are not grouped close to one another, they cannot all be close to the bullseye. (Their [[average]] position might be an accurate estimation of the bullseye, but the [[individual]] arrows are inaccurate.) See also circular error probable for application of precision to the [[science]] of [http://en.wikipedia.org/wiki/Ballistics ballistics].[http://en.wikipedia.org/wiki/Accuracy_and_precision]
[[Category: General Reference]]
