August 21, 2020

One of the first things taught in introductory statistics textbooks is that correlation is not causation. It is also one of the first things forgotten.

One of the first things taught in introductory statistics textbooks is that correlation is not causation. It is also one of the first things forgotten.

Correlation ≠ Causation

I have lost count at the number of times I have rolled my eyes since the outbreak of COVID-19 at someone falling into the logical fallacy Professor Sowell1 reminds us of in this quote.  Cases or fatalities or hospitalizations will go up or down for a few days and someone on social media will immediately claim their favorite theory about the virus has been validated.

Few weeks ago, I saw a person post on Facebook that if the United States had just worn masks and done extensive testing and skip tracing like South Korea and other Asian countries did, the virus’ impact here would have been as low as in those countries.  This is a particularly interesting, and a fairly common, example of confusing correlation and causation, because it is almost certainly partially valid.

Common sense, intuition, and historical experience tell us the masks impede the spread of a respiratory pathogen and quarantine has been recognized since Biblical times as tactic to reduce the spread of an infectious disease.2  But does it follow that masks and better testing and skip tracing could account for a 50-100X difference the cumulative fatality rate between Asian countries and U.S. or Europe?

Almost certainly not.  Emerging research is finding other possible and likely far more potent causes for the different outcomes.

First, some researchers have found evidence that the COVID virus mutated after it left Asia into a more contagious strain.  An article in Biospace magazine summarizes the research that found the new strain is ten times more contagious than the original strain.  Hyeryun Choe, who lead the research for the Scripps Research Institute is quoted in the article saying, “The epidemiological study and our data together really explain why the [G variant’s] spread in Europe and the US was really fast. … This is not just accidental.”

Also, researchers have increasingly found evidence that there is a wide variation between individuals’ susceptibility to COVID and that some regions in the world are less susceptible to contracting the disease.  One study found that some global regions, especially southeast Asia, may have greater resistance to COVID based on greater exposure to previous coronaviruses.  Other research has indicated that some Asians may have a genetic variation in their immune system that provides an advantage in resisting the disease.

And these are just two of a host of other cultural, dietary and sociological differences between countries that can dramatically affect the course of any disease.  A global pandemic is one of the most complex phenomenon in nature.  Any attempt to explain the course of one by simplistic correlations or a single factor or even a small number of factors is naïve in the extreme and disrespects that complexity.

I recently watched a lecture by a Johns Hopkins professor who said that ten years from now we will still be trying to figure out what happened in this pandemic.  I think his estimate might be overly optimistic.


No. 1 – I have  been reading Thomas Sowell for years.  His Basic Economics is still my go-to for economics.  However, prior to finding this quote I did not know anything about his background which turns out to be quite remarkable and inspiring.  His father died shortly was born and was forced to drop out of high school because of the family exigencies.  After serving in the Korean War he attended Howard University and then Harvard were he was graduated magna cum laude.  For more on his life – see Wikipedia.

No. 2 – Leviticus 13:4 – “If the shiny spot on the skin is white but does not appear to be more than skin deep and the hair in it has not turned white, the priest is to isolate the affected person for seven days.”

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