Unless I am missing it, I don't see the actual data anywhere in the paper or supplementary material. Just plots. So we have to eyeball the mean and standard deviation and guess at whether the differences are statistically significant. Given the higher standard deviation in droplet count with the fleece (compared to no mask), it's possible that there is not a statistically significant difference between the two means. I don't think that's an nefarious omission on the part of the authors. They state that the goal was to present a low-cost method for testing mask effectiveness, not to test the effectiveness of the included masks.Originally Posted by Tod-13
"We have demonstrated a simple optical measurement method to evaluate the efficacy of masks to reduce the transmission of respiratory droplets during regular speech."
"Again, we want to note that the mask tests performed here (one speaker for all masks and four speakers for selected masks) should serve only as a demonstration. Inter-subject variations are to be expected, for example due to difference in physiology, mask fit, head position, speech pattern, and such."
"In summary, our measurements provide a quick and cost-effective way to estimate the efficacy of masks for retaining droplets emitted during speech for droplet sizes larger than 0.5 μm. Our proof-of-principle experiments only involved a small number of speakers, but our setup can serve as a base for future studies with a larger cohort of speakers and checks of mask performance under a variety of conditions that affect the droplet emission rate, like different speakers, volume of speech (15), speech patterns (16), and other effects. This method can also test masks under other conditions, like coughing or sneezing. Improvements to the setup can increase sensitivity, yet testing efficiency during regular breathing likely will require complementing measurements with a conventional particle sizer."
As an interesting point, I noticed that Speaker 4 had a lower droplet count with the bandanna than with the surgical mask (Figure S4). They don't show the data broken down by speaker for the fleece covering, so it's possible that two or three of the speakers had much larger droplet counts and pushed the mean upwards, just as with the bandanna. That's why we like to work with larger samples, which this study does not have, by design.
That said, I find it interesting that the fleece covering appears to produce more and smaller droplets over the average of these four speakers. I'm curious if that would play out over a larger sample of individuals. Anecdotally, I find it much easier to breath with a neck gaiter than a cotton mask, so the results appeal to my intuition. In fact, I've put my neck gaiters up and switched back to cotton and surgical masks until we get more data. Gio's right, though. We are (or at least I am) relaying on intuition to say that more and smaller droplets are necessarily a bad thing. What if that actually makes it easier for UV to kill the virus in the droplets, for example? This is way outside my lane, so those studies may well exist. It's just worth noting that we have not seen that evidence in this discussion. We are taking it as a given.
Another limitation the authors note is that using a cell phone camera limits the size of the droplets they can detect. Let's assume for a moment that more and smaller droplets are in fact a bad thing in that they increase the likely hood of transmitting the virus. What if the other masks produce even more and smaller droplets compared to the fleece precisely because of the increased density of the material? We wouldn't know using the methods in this study. I realize that that's kind of out there. I'm just pointing out the authors' admitted limitations of the study.
/rant off. Back to actually talking about mask comfort, because I still haven't found anything other than a neck gaiter that I can tolerate wearing for hours on end...
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