Do Air Filters Really Improve Student Performance?

Matt Yglesias passes along an interesting study that grew out of the Aliso Canyon natural gas leak, which was big news around here in 2015 as Southern California Gas employees spent months trying to plug a well that had blown out. As a precautionary measure, air filters were installed in schools within five miles of the leak even though measurements showed little deterioration of air quality. This provided Michael Gilraine of New York University with a natural experiment: did the air filters change student performance when you compared schools that were just inside the five-mile boundary with schools that were just outside? Gilraine concludes that the filters had a substantial effect. Here’s the raw data:

Hmmm. I can’t say that I see much difference in student performance between the schools within and without the five-mile boundary. However, that’s because I modified Gilraine’s chart to show just the data points and nothing else. Here’s the original chart:

This is known as a discontinuity test, but you can color me skeptical that there’s anything going on here. The sample size is small (about 20 schools on each side of the boundary); the discontinuity is based on a trendline even though there’s no reason to think that student performance should change with distance; the discontinuities are invisible to the naked eye; and only one of them is statistically significant in the first place—and that one just barely.

I’ve come across these kinds of discontinuity tests before, and I’m usually not very impressed with them unless the discontinuity is fairly large and obvious. That said, this result is intriguing and cries out for a more rigorous followup. Unfortunately, this would be fairly expensive: the filtering system runs about $1,000 per classroom, and in the Aliso Canyon schools the cost came to about $100,000 per school. Are there any billionaires out there who’d like to fund this?

AN IMPORTANT UPDATE

We’re falling behind our online fundraising goals and we can’t sustain coming up short on donations month after month. Perhaps you’ve heard? It is impossibly hard in the news business right now, with layoffs intensifying and fancy new startups and funding going kaput.

The crisis facing journalism and democracy isn’t going away anytime soon. And neither is Mother Jones, our readers, or our unique way of doing in-depth reporting that exists to bring about change.

Which is exactly why, despite the challenges we face, we just took a big gulp and joined forces with the Center for Investigative Reporting, a team of ace journalists who create the amazing podcast and public radio show Reveal.

If you can part with even just a few bucks, please help us pick up the pace of donations. We simply can’t afford to keep falling behind on our fundraising targets month after month.

Editor-in-Chief Clara Jeffery said it well to our team recently, and that team 100 percent includes readers like you who make it all possible: “This is a year to prove that we can pull off this merger, grow our audiences and impact, attract more funding and keep growing. More broadly, it’s a year when the very future of both journalism and democracy is on the line. We have to go for every important story, every reader/listener/viewer, and leave it all on the field. I’m very proud of all the hard work that’s gotten us to this moment, and confident that we can meet it.”

Let’s do this. If you can right now, please support Mother Jones and investigative journalism with an urgently needed donation today.

payment methods

AN IMPORTANT UPDATE

We’re falling behind our online fundraising goals and we can’t sustain coming up short on donations month after month. Perhaps you’ve heard? It is impossibly hard in the news business right now, with layoffs intensifying and fancy new startups and funding going kaput.

The crisis facing journalism and democracy isn’t going away anytime soon. And neither is Mother Jones, our readers, or our unique way of doing in-depth reporting that exists to bring about change.

Which is exactly why, despite the challenges we face, we just took a big gulp and joined forces with the Center for Investigative Reporting, a team of ace journalists who create the amazing podcast and public radio show Reveal.

If you can part with even just a few bucks, please help us pick up the pace of donations. We simply can’t afford to keep falling behind on our fundraising targets month after month.

Editor-in-Chief Clara Jeffery said it well to our team recently, and that team 100 percent includes readers like you who make it all possible: “This is a year to prove that we can pull off this merger, grow our audiences and impact, attract more funding and keep growing. More broadly, it’s a year when the very future of both journalism and democracy is on the line. We have to go for every important story, every reader/listener/viewer, and leave it all on the field. I’m very proud of all the hard work that’s gotten us to this moment, and confident that we can meet it.”

Let’s do this. If you can right now, please support Mother Jones and investigative journalism with an urgently needed donation today.

payment methods

We Recommend

Latest

Sign up for our free newsletter

Subscribe to the Mother Jones Daily to have our top stories delivered directly to your inbox.

Get our award-winning magazine

Save big on a full year of investigations, ideas, and insights.

Subscribe

Support our journalism

Help Mother Jones' reporters dig deep with a tax-deductible donation.

Donate