I would also think there is a bias of schools spending extra money and effort towards student improvements if they are willing to go so far as allocate funding for air filtration systems. A better method would be to just give some schools air filtration for free and see if things help without any other major changes.
To me its like looking at schools that buy newer buses and trying to show new buses improve test scores. When in practice the only schools that are buying any significant number of new buses have far more money coming in than in the past and have a lot more to spend on students compared to other schools, which is way more relevant than what year a kid's bus is made. Maybe better buses would improve scores too, but there is no way to tell if 95% of an improvement is due to other unrelated factors based on funding.
> A better method would be to just give some schools air filtration for free and see if things help without any other major changes.
This is what the study looked at.
The problem was that it wasn’t randomized within schools or across teachers. They also looked at a very limited time window. They also note that some teachers weren’t using the air filters. They also found that the VOCs they were trying to filter weren’t even detected before the filters were used. They also used some questionable regressions to imply larger trends.
The list of problems goes on and on. It’s fascinating how easily people are tricked into pivoting around this one study, though, simply because it’s the one introduced by the headline.
> They also looked at a very limited time window. They also note that some teachers weren’t using the air filters.
To correct and clarify:
They also looked at a very limited time window. They also note that-- after this very limited time window-- some teachers stopped using the air filters. In the words of the authors, this made long-run results "difficult to interpret."
To me its like looking at schools that buy newer buses and trying to show new buses improve test scores. When in practice the only schools that are buying any significant number of new buses have far more money coming in than in the past and have a lot more to spend on students compared to other schools, which is way more relevant than what year a kid's bus is made. Maybe better buses would improve scores too, but there is no way to tell if 95% of an improvement is due to other unrelated factors based on funding.