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

How to Spot Visualization Lies

Many charts don’t tell the truth. This is a simple guide to spotting them.

Top Brewery Road Trip, Routed Algorithmically

There are a lot of great craft breweries in the United States, but there is only so much time. This is the computed best way to get to the top rated breweries and how to maximize the beer tasting experience. Every journey begins with a single sip.

Unemployment in America, Mapped Over Time

Watch the regional changes across the country from 1990 to 2016.

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 …