On: Over 80% of Covid-19 patients in a hospital study ...

[nabla9]

Majority of covid-19 hospital patients are elderly. As you get older, your ability to absorb vitamin D decreases.

You must adjust for age.

[spikels → nabla9]

What do you think "population-based controls" means?

[graeme → spikels]

It means the control group: those not hospitalized with covid 19. This is a distinct idea from controlling for confounding factors.

They may have done that too for all relevant factors but we’d need to read the paper.

[watwut → graeme]

Then read the paper.

[nabla9 → spikels]

Covid-19 patient data is not population based.

[joshuamorton → nabla9]

"population based" means that the control population is adjusted to match the experiment population.

In other words, you could read the line as "Vitamin D deficiency was found in 82.2% of COVID-19 cases and 47.2% of controls, when accounting for age (p<0.0001)."