WSJ: “It’s Dangerous to Test Only the Sick”

Earlier this week, we posted Let’s make COVID testing actionable, providing a decision matrix and arguing that asymptomatic people (boxes A and C below) should be tested to determine if they are “hidden carriers” who should be quarantined.


Complementing our post, the WSJ published a piece arguing that “It’s Dangerous to Test Only the Sick

Its punch line: Random sampling is essential to learn the truth about virus spread and deadliness.

Let’s drill down on that…


The author argues that testing has two purposes apart from diagnosing individual cases:

The first is to obtain accurate information on the virus’s infectivity and mortality rates.

Testing only sick or symptomatic patients will not get us to the truth.

Testing only sick and symptomatic people will result in an overestimate of mortality, which would heighten fear and anxiety and worsen their economic effects.

The second purpose of testing is to avert spread by isolating those who are infected.

In this regard, it is unclear that relying exclusively on people who are volunteering for the tests makes sense.

These are probably people who are exhibiting symptoms and already heeding public-health messages to isolate themselves at home.

A study of flu-vaccine strategies shows that self-selection doesn’t get at the high-risk populations.

So, what to do?

If it were feasible, data scientists would love to test everybody to determine how many people are infected. how many are symptomatic and how many get treated and how many succumb to the disease.

Testing everybody isn’t feasible (and, would even be illegal if it’s coerced.

So, the author recommends:

The way to learn the truth is to test a random sample of the population in major cities with an outbreak.

Random testing would reveal the true mortality rate and also how many people have the virus, an important factor in determining its infectivity.

A good strategy would be to combine drive-thru tests with targeted testing of high-risk populations to try to catch people who are unwittingly spreading coronavirus.

I agree!


Follow on Twitter @KenHoma

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One Response to “WSJ: “It’s Dangerous to Test Only the Sick””

  1. Senate may be starting to ask the right questions re: testing. | The Homa Files Says:

    […] WSJ: “It’s Dangerous to Test Only the Sick” […]

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