Clarify underreporting methodology

[velocitybucket]

From reading the whitepaper, it seems that the underreporting factor is sometimes 6x, but other times it is determined by the "Covid-19 Projections" factor of 1250/(day_i+25)*positive_test_rate**0.5+2. But what determines whether or not a 6x factor is used? It seems to be a function of the test positivity rate, but what is the function?

Note that this question is not answered in the whitepaper. Rather, the whitepaper seems to incorrectly state that the minimum underreporting factor is 6. But the formula 1250/(day_i+25)*positive_test_rate**0.5+2 is bounded within 2.0 and 3.5, so this formula would never be used if the underreporting factor is always set to a minimum of 6. Moreover, by inspecting the calculations made by the calculator, it does not seem that 6 is always used.

[apiology]

Hi @velocitybucket! Sorry for the slow reply - we've been a little light on contributors lately. If you're interested in digging in on this with me on a Zoom call or something like that, please reach out - I should be able to help tease through the code to clarify this and update code/docs as needed.