> What about things other than ammonia? Certainly possible, but it seems more likely that the control group would have been exposed to something harmful from t

> What about things other than ammonia? Certainly possible, but it seems more likely that the control group would have been exposed to something harmful from the lab environment air versus the CO2 group that was getting medical air. > And did they have a "good" fan, or a bad fan? The cheapest 80mm fan I can find on newegg.com is a $3.49 Zalman[1] that is 20-23 dBA. That's comparable to the sound of rustling leaves and far less than the sound of a quiet whisper (30 dBA) or a babbling brook (40 dBA). Someone would have to go out of their way to find an 80mm fan that is so bad that it would be louder than a natural environment. > The point of making the environment for the exposure and control groups be as near identical as possible is to equalize not only the factors you thought of, but also the factors you didn't think of. I completely agree. I don't recall seeing a paper I couldn't poke holes in though. The fact that their methods were imperfect does not make the study worthless. They found a modest effect for the given methods. It suggests there may be merit to follow-on studies, which would likely use different methods. That's a useful result that has added new information. [1] https://www.newegg.com/zalman-f1-led-case-fan/p/N82E16835118154 https://www.newegg.com/zalman-f1-led-case-fan/p/N82E16835118...