McHugh David: Percent positivity doesn’t work when sample size is so low

The difficulty with a pandemic is the double-edged sword of understanding why there are mitigation efforts and why one must be cautious during this time, but being equally frustrated with gating methods.

Take the ‘percent positivity’ method for determining when bars can open, for instance. As of right now, each parish faces the requirement that, for a two week period, the number of positive COVID-19 tests that come back must be less than five percent of the total take.

On it’s face, it appears to be a good idea. Finding the criteria that shows an amount of ‘active COVID’ in any given population gives an appropriate ‘top down’ metric for seeing how wide spread (or not so wide spread) the virus is in any given community.

The state even breaks down the percent positivity rate by parish, allowing smaller locales to have more control over when their bars and watering holes are allowed to open.

Unfortunately, that’s about where the good news stops.

From a statistical standpoint, percent positivity doesn’t paint the real picture. The number of positive tests that come back on any given sample really just shows the number of people who were feeling sick.

Or, in today’s world, the number of people who were sick enough to qualify for a test. As of right now, tests are in short supply according to reports, and most doctors won’t approve one unless you’re showing enough symptoms to warrant one.

Otherwise – if you come in contact with someone with COVID-19 or show mild symptoms, quarantine for 14 days.

This general set of circumstances is unfortunate, because what it really adds up to is the sample size simply isn’t large enough to be accurate.

Not convinced? Consider it in terms of just one high school. Imagine if there was one class, of whom a single individual tested positive. Everyone in the class was informed, quarantined, and the crisis is now over.

Or is it?

What about the teachers who interacted with that one? What about the other classes in the grade? What about the other grades?

Get the picture?

The secondary unfortunate part of all this is this statement – while the entire circumstance of percent positivity doesn’t really pan out, there’s really no better way. Why? Because we don’t have the money for it, as a country.

This has been discussed, several times, since the part of the pandemic. The reason stimulus packages haven’t been doled out is partly political, that much is true, but the rest of it boils down to money. The United States was riding high on credit and easing up against the tipping point of debt-to-revenue ratio. With COVID reeking havoc on the economy, it’s expected the country will default on some of its debt in 2021.

In the end, it remains a double-edged sword because while the country cannot afford to test everyone, all the time, have a true sense of how much COVID is out there, there’s also not a better gating option to be found.

McHugh David is publisher of the Livingston Parish News.