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COVID-19 and Vitamin D – data vs noise in science


The COVID-19 crisis creates a useful illustration:

Two groups of researchers recently reported a link between vitamin D and COVID-19 mortality—more vitamin D meant lower mortality. A Northwestern University researcher who reported this association advised that “it is clear that vitamin D deficiency is harmful, and it can be easily addressed with appropriate supplementation.”

Gary Smith, “Vitamin D and Covid-19: Is it Data or Noise?” at Mind Matters News

Cue media frenzy. The trouble is, as statistics analyst Gary Smith of Pomona College points out,

One very big problem with such studies is the inevitability of chance patterns and correlations in large data bases. Even if COVID-19 deaths are randomly distributed among the population (and they surely aren’t), data mining will, more likely than not, discover a geographic cluster of victims…

Gary Smith, “Vitamin D and Covid-19: Is it Data or Noise?” at Mind Matters News

He created a fictitious city to illustrate the point:

The same argument scales up to cities within a country or countries within the world. Some cities will inevitably have higher COVID-19 rates than others; so will some countries. So what? Because random data contain geographic clusters, the identification of clusters is not necessarily meaningful. The association, after the fact, of these clusters with some characteristics of the area or the people living in the area is not convincing scientific evidence of anything.

Gary Smith, “Vitamin D and Covid-19: Is it Data or Noise?” at Mind Matters News

See also: Data mining: A plague, not a cure. It is tempting to believe that patterns are unusual and their discovery meaningful; in large data sets, patterns are inevitable and generally meaningless. (Gary Smith)

Polistra - I assume you're joking, sometimes it's difficult to work out online. Bob O'H
From the newly released study: “Our finding suggests that Vit D may reduce COVID-19 severity by suppressing cytokine storm in COVID-19 patients,” researchers from Northwestern University wrote. From an article: "The study, which was led by researcher Ali Daneshkhah, determined that the risk of severe COVID-19 cases among patients with severe vitamin deficiency is 17.3 percent. The equivalent figure for patients with normal vitamin D levels was 14.6 percent." This statistical distance does look pretty small; it may pass the significance criterion, but it isn't impressive. There is the random fluctuation in large samples hypothesis. On the other hand, it costs very little to take a 3000-4000 IU vitamin D3 capsule every day as a precaution just in case. doubter
In this case we don't even need to think about the stats. Just syllogistic logic. We've known for decades that viruses don't thrive in sunlight. This virus is a virus, therefore it doesn't thrive in sunlight. polistra

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