Simpson's: It was first mentioned by British statistician Udny Yule in 1903.
A paradox: Simpson's paradox is just a special case of ommitted variable bias. W.V. Quine would call it a veridical paradox.
Every ommitted variable problem: Women earn only 77 percent of what men do, but according to Cornell economists Francine Blau and Lawrence Kahn, accounting for work experience, education, industry, and unionization shrinks the gap to 91 percent (p. 52). So, discrimination matters less than the `77 percent` stat would lead you to believe. But is this Simpson's paradox? No, because the correction isn't large enough for the effect of gender to change sign.
Simpson's paradox usually fools us on tests of performance. In a famous example, researchers concluded that a newer treatment for kidney stones was more effective than traditional surgery, but it was later revealed that the newer treatment was more often being used on small kidney stones. More recently, on elementary school tests, minority students in Texas outperform their peers in Wisconsin, but Texas has so many minority students that Wisconsin beats it in state rankings. It would be a shame if Simpson's paradox led doctors to prescribe ineffective treatments or Texas schools to waste money copying Wisconsin.
A project of the Visualizing Urban Data ideaLab at UC Berkeley. Created in d3.js and AngularJS by Lewis Lehe and Victor Powell. Lewis Lehe is a PhD student in Transportation Engineering at UC Berkeley, and Victor Powell is a freelance developer, JavaScript instructor and yinzer.