Imagine you were the mayor of a small city at the beginning of the pandemic. You are considering whether to impose a requirement for people to wear masks in public places. You've read opinions for and against, but you want your own evidence about whether such a mandate would really stop the virus. Which of the following would be the best way to gather such evidence?
a. Find a city close to yours that implemented a mask mandate to see if the infection rate declined after the mandate went into effect. If the rate declined then you know the mandates work if not you will know they do not work.
b. Wear a mask yourself to see if you get infected. If you don't get sick, then you would have good reason to implement such a policy.
c. Set up two groups of people: one group wears masks while the others group does not. Then expose both groups to the virus. If the group wearing masks has fewer infections, then you know for sure that masks work.
d. Identify other cities of similar size as yours and compare the infection rate of those that did and did not impose such mandates. If the infection rate significantly lower in the cities with mask mandates you could reasonably conctude that the masks were the only relevant difference in the cities, and thus, Bely the cause of the lower infection rate.
e. Implement the mask mandate and watch the infection rate for several weeks: if it decreases then you know the mandate works.