For the eleventh day of mask mess, we got these:

Fischer et al.

Low-cost measurement of face mask efficacy for filtering expelled droplets during speech. Science Advances (2020).

Submitted June 12, 2020, this study tests “14 commonly available masks or mask alternatives, one patch of mask material, and a professionally fit-tested N95 mask.” The masks are tested using an operator wearing a face mask and saying “Stay healthy, people” five times in the direction of a laser beam. As the speaker’s emitted droplets scatter light, it is recorded by a standard cell phone camera. “This experimental setup is simple and can easily be built and operated by nonexperts,” according to Fischer et al.

That is an important key because this study is not about determining what face masks governments should mandate. It is to test out a method for evaluating face masks given such government mandates. Fischer et al. write that theirs is not a “comprehensive survey of all possible mask designs” nor a “systematic study of all use cases.” Instead, they note, “We merely demonstrated our method on a variety of commonly available masks and mask alternatives with one speaker, and a subset of these masks were tested with four speakers.” These were, they write, “limited demonstration studies.” And from this perspective, “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 5µm.”

The reason for the study is that,

Mandates for mask use in public during the recent coronavirus diseases 2019 (COVID-19) pandemic, worsened by global shortage of commercial supplies, have led to widespread use of homemade masks and mask alternatives. It is assumed that wearing such masks reduces the likelihood for an infected person to spread the disease, but many of these mask designs have not been tested in practice.

In other words, this study begins with the assumption of a mask mandate and widespread use of homemade masks. Fischer et al. are interested in addressing the need for simple and nonexpert methods of testing mask efficacy.

Through their limited demonstration studies, Fischer et al. observe a wide range in mask efficacy, with some offering droplet reduction (as measured via cell phone camera) near that of N95 and surgical masks, but some others being close to not wearing a mask at all (neck gaiters seemed to disperse droplets into smaller droplets, for example).

Does this study support Cooper’s extreme exercise of power?


Taking a study that starts by assuming a mask order in place cannot justify a mask order. Circular reasoning is no basis for an extreme emergency order.

Going further, this study offers “limited demonstration studies” to find simple ways for nonexperts to test mask efficacy. None of that makes it appropriate for use to justify an extreme emergency order.

Bae et al.

Effectiveness of Surgical and Cotton Masks in Blocking SARS–CoV-2: A Controlled Comparison in 4 Patients. Annal of Internal Medicine (2020).

Published online on April 6, 2020, this article was retracted. See the Notice of Retraction here.

Does this study support Cooper’s extreme exercise of power?


A retracted study must never serve as the basis of an extreme emergency order.

Click for more of the Twelve Days of Mask Mess series.