A visual explanation of Simpson’s Paradox

Posted to Statistics  |  Tags:  |  Nathan Yau

When you look for overall trends, you often poke around the data in aggregate, but when you zoom out too far, you could miss details or within-category variation. Sometimes when you zoom in, you see a completely opposite trend of what you saw overall. This is known as Simpson’s Paradox. Lewis Lehe and Victor Powell explain in a series of small, interactive charts.

Why does this matter?

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.

The takeaway lesson: Remember to look at the details. [Thanks, Victor]

Favorites

The Best Data Visualization Projects of 2014

It’s always tough to pick my favorite visualization projects. Nevertheless, I gave it a go.

Real Chart Rules to Follow

There are rules—usually for specific chart types meant to be read in a specific way—that you shouldn’t break. When they are, everyone loses. This is that small handful.

Famous Movie Quotes as Charts

In celebration of their 100-year anniversary, the American Film Institute selected the 100 most memorable quotes from American cinema, and …

The Most Unisex Names in US History

Moving on from the most trendy names in US history, let’s look at the most unisex ones. Some names have …