Saturday, April 4, 2020

What's Wrong with this Reasoning?


  1. FACT: the population density of NYC is 27K per square mile
  2. FACT: the population density of Indianapolis is 2K per square mile
  3. FACT: COVID-19 was able to be introduced and spread in a city with only 2K susceptible people per square mile (Indianapolis is such a city).
Conclusion: COVID-19 will continue to spread in NYC until either (i) the number of susceptible people falls to 2K per square mile or (ii) a vaccine.  i.e., until more than 90% of NYC has contracted and recovered from COVID-19.  [This conclusion says nothing about time frame; i.e., it could be years]

Does the conclusion follow from the three facts?
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2 comments:

  1. Danley WolfeApril 5, 2020 at 9:17:00 AM CDT

    Of course not. The logical progression of "if A then B" does not allow one to make a leap to a completely different comparison without taking into account ALL OTHER FACTORS that are active / in play such as mitigation, population characteristics of the different comparison groups (ethnicity, age distribution, previous exposure i.e., immunity, others ... But you might see such logic on some of mainstream news programs.

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  2. Macro GuyApril 6, 2020 at 2:48:00 PM CDT

    You have an implicit assumption that people interact with a number of others proportional to population density. This isn't true. The number of interactions is higher in NYC, but not that much higher.

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