Median: Difference between revisions

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This set contains seven numbers. The median is the fourth of them, which is 6.
 
If there is an even number of observations, then there is no single middle value; the median is then usually defined to be the [[arithmetic mean|mean]] of the two middle values.<ref name="StatisticalMedian">{{MathWorld |urlname=StatisticalMedian |title=Statistical Median }}</ref><ref>Simon, Laura J.; [http://www.stat.psu.edu/old_resources/ClassNotes/ljs_07/sld008.htm "Descriptive statistics"] {{webarchive|url=https://web.archive.org/web/20100730032416/http://www.stat.psu.edu/old_resources/ClassNotes/ljs_07/sld008.htm |date=2010-07-30 }}, ''Statistical Education Resource Kit'', Pennsylvania State Department of Statistics</ref> For example, in the data set
 
: 1, 2, 3, 4, 5, 6, 8, 9
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Any [[Bias of an estimator|''mean''-unbiased estimator]] minimizes the [[risk]] ([[expected loss]]) with respect to the squared-error [[loss function]], as observed by [[Gauss]]. A [[Bias of an estimator#Median unbiased estimators.2C and bias with respect to other loss functions|''median''-unbiased estimator]] minimizes the risk with respect to the [[Absolute deviation|absolute-deviation]] loss function, as observed by [[Laplace]]. Other [[loss functions]] are used in [[statistical theory]], particularly in [[robust statistics]].
 
The theory of median-unbiased estimators was revived by [https://web.archive.org/web/20110310043642/http://www.universityofcalifornia.edu/senate/inmemoriam/georgewbrown.htm George W. Brown] in 1947:<ref name="Brown" />
 
{{quote|An estimate of a one-dimensional parameter θ will be said to be median-unbiased if, for fixed θ, the median of the distribution of the estimate is at the value θ; i.e., the estimate underestimates just as often as it overestimates. This requirement seems for most purposes to accomplish as much as the mean-unbiased requirement and has the additional property that it is invariant under one-to-one transformation.|page 584}}