The coverage of the COVID-19 epidemic always focuses on the number of cases diagnosed. See for example, the excellent dashboard continually updated by our colleagues at Johns Hopkins: https://coronavirus.jhu.edu/map.html
The case count is important because it is a measure of the potential burden on the healthcare system.
But we also create communication problems when we talk about the case count (the numerator) without also mentioning the denominator (the population). Notice how different these statements — all mathematically true — feel to you:
>”There are 10,000 confirmed COVID-19 cases in NYC.”
>”There are 10,000 confirmed COVID-19 cases among the 8 million people in NYC.”
>”There are 125 COVID-19 cases for every 100,000 New Yorkers.”
>”There is about 1 COVID-19 case for every 1000 New Yorkers.”
We should be intentional in our choices of numbers to talk about. We should be aware that showing the numerator alone, without also talking about the denominator, tends to inflate concern and motivation to act. Although this might seem justifiable in the current situation, we need to recognize that doing so will tend to reduce our audiences’ understanding of the actual magnitude of the issue.
A good study on this topic was recently published by Eric Stone at Wake Forest University. https://www.tandfonline.com/doi/abs/10.1080/10810730.2015.1018594
Making Numbers Meaningful 