- Histogram
In

statistics , a**histogram**is agraphical display of tabulated frequencies, shown asbar s. It shows what proportion of cases fall into each of several categories. A histogram differs from abar chart in that it is the "area" of the bar that denotes the value, not the height, a crucial distinction when the categories are not of uniform width (Lancaster, 1974). The categories are usually specified as non-overlappinginterval s of some variable. The categories (bars) must be adjacent.The word "histogram" is derived from Greek: "histos" 'anything set upright' (as the masts of a ship, the bar of a loom, or the vertical bars of a histogram); "gramma" 'drawing, record, writing'. The histogram is one of the seven basic tools of quality control, which also include the

Pareto chart ,check sheet ,control chart ,cause-and-effect diagram ,flowchart , andscatter diagram . A generalization of the histogram is kernel smoothing techniques. This will construct a very smoothprobability density function from the supplied data.**Examples**As an example we consider data collected by the U.S. Census Bureau on time to travel to work (2000 census, [

*http://www.census.gov/prod/2004pubs/c2kbr-33.pdf*] , Table 5). The census found that there were**124 million people**who work outside of their homes. This rounding is a common phenomenon when collecting data from people..$h(f)(y)$ is undefined if $y$ is the value of a

stationary point .**ee also***

Density estimation

*Freedman-Diaconis rule

*Image histogram

*Kernel density estimation , another method of visualizing probability density functions that can be preferred to histograms.**Notes****References***

Webster's Third New International Dictionary , "Merriam-Webster; Ind Una edition (June 2002)".

* Lancaster, H.O. "An Introduction to Medical Statistics." John Wiley and Sons. 1974. ISBN 0 471 51250-8**External links*** [

*http://www.census.gov/population/www/socdemo/journey.html Journey To Work and Place Of Work*] "(location of census document cited in example)"

* [*http://www.luminous-landscape.com/tutorials/understanding-series/understanding-histograms.shtml Understanding histograms in digital photography*]

* [*http://quarknet.fnal.gov/toolkits/ati/histograms.html Histograms: Construction, Analysis and Understanding with external links and an application to particle Physics.*]

* [*http://www.ton.scphys.kyoto-u.ac.jp/~hideaki/res/histogram.html A Method for Selecting the Bin Size of a Histogram*]

* [*http://www.shodor.org/interactivate/activities/histogram/ Interactive histogram generator*]

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