Ask HN: How are we modeling the outbreak?

Some U.S. states are now telling their citizens that they don’t need to be tested for COVID-19 except after consulting with a physician.

The U.S. government and media are reporting confirmed cases (an absolute number).

It seems like the government is using a statistical model to quantify the number of infected without testing. Does anyone here know what the model is? If not, are there models that are likely to be used in this case?