Editing Francis Galton (section)

===Variance and standard deviation===
Core to any statistical analysis is the concept that measurements vary: they have both a [[central tendency]], or mean, and a spread around this central value, or [[variance]]. In the late 1860s, Galton conceived of a measure to quantify normal variation: the [[standard deviation]].<ref>{{cite web|author=Chad Denby |url=http://www.sciencetimeline.net/1866.htm |title=Science Timeline |publisher=Science Timeline |access-date=22 April 2013}}</ref>

Galton was a keen observer. In 1906, visiting a livestock fair, he stumbled upon an intriguing contest. An ox was on display, and the villagers were invited to guess the animal's weight after it was slaughtered and dressed. Nearly 800 participated, and Galton was able to study their individual entries after the event. Galton stated that "the middlemost estimate expresses the ''vox populi'', every other estimate being condemned as too low or too high by a majority of the voters",{{sfn|Galton|1907|p=450}} and reported this value (the [[median]], in terminology he himself had introduced, but chose not to use on this occasion) as 1,207 pounds. To his surprise, this was within 0.8% of the weight measured by the judges. Soon afterwards, in response to an enquiry, he reported<ref>"[http://galton.org/cgi-bin/searchImages/galton/search/essays/pages/galton-1907-ballot-box_1.htm The Ballot Box]", ''Nature'', 28 March 1907</ref> the mean of the guesses as 1,197 pounds, but did not comment on its improved accuracy. Recent archival research{{sfn|Wallis|2014|pp=420–424}} has found some slips in transmitting Galton's calculations to the original article in ''Nature'': the median was actually 1,208 pounds, and the dressed weight of the ox 1,197 pounds, so the mean estimate had zero error. James Surowiecki{{sfn|Surowiecki|2004|p=}} uses this weight-judging competition as his opening example: had he known the true result, his conclusion on the [[wisdom of the crowd]] would no doubt have been more strongly expressed.

The same year, Galton suggested in a letter to the journal ''[[Nature (journal)|Nature]]'' a better method of cutting a round cake by avoiding making radial incisions.{{sfn|Galton|1906|p=173}}