There are many things we would like to know about the novel coronavirus but don’t.

How many cases are out there? Are we testing enough? How could we tell if we were testing enough?

Epidemiologists say looking at the ratio of positive tests to deaths gives us about as good an idea as we’re likely to get.

In general, the higher the number of tests in relation to each death, the better the surveillance is, and the better the chance that it’s finding people who are asymptomatic. The lower the number, the better the chance that only a few of the most obvious cases are being found.

Positive tests per death are a measure of how thorough testing is in a place in relation to the size of the problem.

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“Having more tests per death suggests that you are finding more of the less severe infections,” says Ashleigh Tuite, an epidemiologist at the University of Toronto. “It means that you probably have a better view of what is going on in terms of the amount of disease that’s in your population.