Editing Simpson's paradox (section)

==Correlation between variables==
Simpson's reversal can also arise in [[correlation]]s,  in which two variables appear to have (say) a positive correlation towards one another, when in fact they have a negative correlation, the reversal having been brought about by a "lurking" confounder.  Berman et al.<ref>Berman, S. DalleMule, L.  Greene, M., Lucker, J. (2012), "[http://www.statslife.org.uk/the-statistics-dictionary/2012-simpson-s-paradox-a-cautionary-tale-in-advanced-analytics Simpson's Paradox: A Cautionary Tale in Advanced Analytics] {{Webarchive|url=https://web.archive.org/web/20200510171740/https://www.statslife.org.uk/the-statistics-dictionary/2012-simpson-s-paradox-a-cautionary-tale-in-advanced-analytics |date=2020-05-10 }}", ''[[Significance (magazine)|Significance]]''.</ref> give an example from economics, where a dataset suggests overall demand is positively correlated with price (that is, higher prices lead to ''more'' demand), in contradiction of expectation.   Analysis reveals time to be the confounding variable: plotting both price and demand against time reveals the expected negative correlation over various periods, which then reverses to become positive if the influence of time is ignored by simply plotting demand against price.