7/31/2019 Accuracy and Precision - Wikipedia, The Free Encyclopedia

1/4

Acc uracy indicates proximity of measurementresults to the true value, precision to therepeatability or reproducibility of the measurement

High accuracy , but lowprecision

High precision but lowaccuracy

Accuracy and precisionFrom Wikipedia, the free encyclopedia

In the fields of science, engineering, industry and statistics, the accuracy [1] of a measurement system is the degree of closeness of measurements of a quantity tothat quantity's actual (true) value. The precision [1] of a measurement system, also called reproducibility or repeatability, is the degree to which repeatedmeasurements under unchanged conditions show the same results. [2] Although the two words reproducibility and repeatability can be synonymous in colloquialuse, 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 end 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) anderror (random variability).

The terminology is also applied to indirect measurementsthat 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 thesmallest 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 toreproducibility. 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 withwhich an arbitrary number can be represented.

Contents

1 Accuracy versus precision: the target analogy2 Quantifying accuracy and precision3 Accuracy and precision in binary classification4 Accuracy and precision in psychometrics and psychophysics5 Accuracy and precision in logic simulation6 Accuracy and precision in information systems7 See also

8 References9 External links

Accuracy versus precision: the target analogy

Accuracy is the degree of veracity while in some contexts precision may mean the degree of reproducibility. [citation needed ]

The analogy used here to explain the difference between accuracy and precision is the target comparison. In this analogy, repeatedmeasurements are compared to arrows that are shot at a target. Accuracy describes the closeness of arrows to the bullseye at the targetcenter. 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 isshot, precision is the size of the cluster one would expect if this were repeated many times under the same conditions.) When all arrows aregrouped 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 precisionif the arrows are not grouped close toone another, they cannot all be close to the bullseye. (Their average position might be an accurate estimation of the bullseye, but theindividual arrows are inaccurate.) See also circular error probable for application of precision to the science of ballistics.

Quantifying accuracy and precision

See also: False precision

Ideally a measurement device is both accurate and precise, with measurements all close to and tightly clustered around the known value. Theaccuracy and precision of a measurement process is usually established by repeatedly measuring some traceable reference standard. Such standards are defined in

7/31/2019 Accuracy and Precision - Wikipedia, The Free Encyclopedia

2/4

7/31/2019 Accuracy and Precision - Wikipedia, The Free Encyclopedia

3/4

class is more important, F-measure may be more appropriate, especially in situations with very skewed class imbalance. An alternate performance measure thattreats both classes with equal importance is "balanced accuracy":

Accuracy and precision in psychometrics and psychophysics

In psychometrics and psychophysics, the term accuracy is interchangeably used with validity and constant error . Precision is a synonym for reliability andvariable error . The validity of a measurement instrument or psychological test is established through experiment or correlation with behavior. Reliability is

established with a variety of statistical techniques, classically through an internal consistency test like Cronbach's alpha to ensure sets of related questions haverelated responses, and then comparison of those related question between reference and target population. [citation needed ]

Accuracy and precision in logic simulation

In logic simulation, a common mistake in evaluation of accurate models is to compare a logic simulation model to a transistor circuit simulation model. This is acomparison of differences in precision, not accuracy. Precision is measured with respect to detail and accuracy is measured with respect to reality. [3][4]

Accuracy and precision in information systems

The concepts of accuracy and precision have also been studied in the context of data bases, information systems and their sociotechnical context. The necessaryextension of these two concepts on the basis of theory of science suggests that they (as well as data quality and information quality) should be centered onaccuracy defined as the closeness to the true value seen as the degree of agreement of readings or of calculated values of one same conceived entity, measured or

calculated by different methods, in the context of maximum possible disagreement.[5]

See also

Accuracy classANOVA Gauge R&R ASTM E177 Standard Practice for Use of the Terms Precision and Bias in ASTM Test MethodsExperimental uncertainty analysisFailure assessmentGain (information retrieval)Precision biasPrecision engineeringPrecision (statistics)Accepted and experimental value

References

1. ^ a b JCGM 200:2008 International vocabulary of metrology (http://www.bipm.org/utils/common/documents/jcgm/JCGM_200_2008.pdf) Basic and general concepts and associated terms (VIM)

2. ^ John Robert Taylor (1999). An Introduction to Error Analysis: The Study of Uncertainties in Physical Measurements (http://books.google.com/books?id=giFQcZub80oC&pg=PA128) . University Sc ience Books. pp. 128129. ISBN 0-935702-75-X. http://books.google.com/books?id=giFQcZub80oC&pg=PA128.

3. ^ John M. Acken, Encyclopedia of Computer Science and Technology, Vol 36, 1997, page 281-3064. ^ 1990 Workshop on Logic-Level Modelling for ASICS, Mark Glasser, Rob Mathews, and John M. Acken, SIGDA Newsletter, Vol 20. Number 1, June 19905. ^ Ivanov, K. (1972). "Quality-control of information: On the concept of accuracy of information in data banks and in management information sys tems"

(http://www .informatik.umu.se/~kivanov/diss-avh.html) . The University of Stoc kholm and The Royal Institute of Tec hnology. Doctoral dissertation. Further detailsare found in Ivanov, K. (1995). A subsystem in the design of informatics: Recalling an archetypal engineer. In B.. Dahlbom (Ed.), The infological equation: Essaysin honor of Brje Langefors (http://www .informatik.umu.se/~kivanov/BLang80.html) , (pp. 287-301). Gothenburg: Gothenburg University, Dept. of Informatics(ISSN 1101-7422).

External links

BIPM - Guides in metrology (http://www.bipm.org/en/publications/guides/) - Guide to the Expression of Uncertainty in Measurement (GUM) andInternational Vocabulary of Metrology (VIM)"Beyond NIST Traceability: What really creates accuracy" (http://img.en25.com/Web/Vaisala/NIST-article.pdf) - Controlled EnvironmentsmagazinePrecision and Accuracy with Three Psychophysical Methods (http://www.yorku.ca/psycho)Guidelines for Evaluating and Expressing the Uncertainty of NIST Measurement Results, Appendix D.1: Terminology(http://physics.nist.gov/Pubs/guidelines/appd.1.html)Accuracy and Precision (http://digipac.ca/chemical/sigfigs/contents.htm)

Retrieved from "http://en.wikipedia.org/w/index.php?title=Accuracy_and_precision&oldid=455717934"Categories: Biostatistics Statistical theory Psychometrics Evaluation Critical thinking Qualities of thought Uncertainty of numbers

7/31/2019 Accuracy and Precision - Wikipedia, The Free Encyclopedia

4/4

Measurement Summary statistics for contingency tables

This page was last modified on 15 October 2011 at 17:44.Text is available under the Creative Commons Attribution-ShareAlike License; additional terms may apply. See Terms of use for details.Wikipedia is a registered trademark of the Wikimedia Foundation, Inc., a non-profit organization.