Interpreting rates: COVID-19


This article, from AlJazeera, reminds me of my epidemiology lesson about interpreting rates. Its heading reads as”why Italy’s coronavirus fatality rate is so high”.

First about the concept of a “rate”. A rate has a numerator and a denominator = numerator/denomintor. We multiply the resulting value by either 1000, 10,000, 100,000, or even a million depending on the situation.

In this situation, the denominator is the number of persons tested for the COVID 19 virus. Its numerator is the number of persons reported positive with the test.

I would begin with the order of questions I would ask when I need to interpret a rate.

Question 1: Is there any problem with testing and reporting?

yes; Italy’s denominator (number of infected cases due to their more restrictive case definition) is lower due to fewer testing from other countries such as South Korea and Germany (due to their more liberal case definitions). For example, as of March 15, South Korea has carried out 3,40,000 tests whereas Italy has done only 1,25,000 tests.

Question 2: Is there a demographical variation?

yes, Italy owns the second-highest percentage of seniors (above 65 years) in the world (second only to Japan).

Question 3: Is there any cultural difference?

yes, when compared to other western societies, grandparents are closely connected to their extended family structure – to children and grandchildren. As a result, self-isolation is difficult.

In addition to these reasons, they were late in implementing physical distancing.

This also emphasizes another important aspect of physical distancing: when community spreading occurs, seniors within the family requires physical distancing from their own children who go out.


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