Posted on by Californiacontrarian

The Influence of the Denominator

In the Wall Street Journal on 3/14/20 there was an article comparing the Wuhan flu (coronavirus) in South Korea vs. Italy. The main drift of the article was comparing the populace of an Eastern culture with that of a Western culture. To paraphrase, the influence of Confucianism in Eastern cultures emphasizes respect for authority, and the good of the nation above individualism. In contrast in Western cultures there is widespread skepticism  toward authority. Take for example, the public pressure that forced the relaxing of a 6 p.m. curfew on bars in Milan. Oops!

The other significant thing that I noticed in this article was “ the influence of the denominator,” which turns out to be a very significant influence of any statistics. For those of you who are somewhat math handicapped, I will try to explain. It is actually a very simple concept. Basically, if the denominator increases while the numerator stays the same, the resultant percent decreases. 

Italy and South Korea have comparable populations. although Italy has about 15% more people. . . . Italy = 60 million, South Korea = 52 million. In Italy, initially, testing for the virus was restricted to those with symptoms (about 3,000 tests per day) whereas South Korea was performing more than 15,000 tests per day. The incidence of the Wuhan flu was the following:

Italy = 17,660 cases/ 97,488 tested for incidence of about 18%. So.Korea = 7,979 cases/240,668 tested for incidence of about 3%. So what is the true incidence of infection? . . . it depends on the denominator. Likewise, for the mortality:
Italy = 1,286deaths/17,660 cases for a mortality of about 7%. So. Korea = 67deaths/7,979 cases for a morality of 0.8 %. So what is the true mortality? Here it is a bit more complicated, as it depends on who is included in the denominator. If the denominator includes all of those tested, many of whom were minimally symptomatic or even asymptomatic, (South Korea) then the number of cases in the denominator will be skewed, and the mortality will be much less. Likewise, if the denominator is made up mostly of older, sicker people, (Italy) the denominator will also be skewed, but in the opposite direction. The same will apply here in the U.S. . . . what is the denominator? If, as is the situation in Washington State, the denominator is predominately made up of those in nursing homes and their close contacts, then the mortality will be much higher than the overall mortality once drive-through testing becomes widely available and the denominator is drastically increased.

So how dangerous is this Wuhan flu? It depends on the denominator!

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