What is Accuracy and precision?
[[File:Accuracy and precision.svg|thumb|300px|Accuracy: how close results are to the true value <br/>Precision: the repeatability of measurements]] The '''accuracy and precision''' of [[measurement]]s have special meanings in the fields of [[science]], [[engineering]], [[industry]] and [[statistics]]. *The '''accuracy''' of a measurement system is how close it gets to a [[quantity]]'s actual (true) value.<ref name=metrology_terms> [http://www.bipm.org/utils/common/documents/jcgm/JCGM_200_2008.pdf JCGM 200:2008 International vocabulary of metrology] — Basic and general concepts and associated terms (VIM)</ref> *The '''precision''' of a measurement system is the degree to which repeated measurements give the same results.<ref name=metrology_terms /><ref name=Taylor>{{cite book |title=An Introduction to Error Analysis: The Study of Uncertainties in Physical Measurements |author=John Robert Taylor |url=https://books.google.com/books?id=giFQcZub80oC&pg=PA128 |pages=128–129 |isbn=0-935702-75-X |year=1999 |publisher=University Science Books}}</ref> A measurement system can be accurate but not precise, precise but not accurate, neither, or both. For example, if an [[experiment]] contains a [[error]] in the way it is done, then increasing the [[sample size]] generally increases precision but does not improve accuracy. The end result would be a consistent, yet inaccurate, set of results from the flawed experiment. Eliminating the systematic error improves accuracy but does not change precision. A measurement system is [[validity|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). == Related topics == 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 s