3 ms·

It’s not “correlation at best”. It’s an almost canonical example of the Bayesian error: given a reverse probability (if you’re sick => you’re 80% likely to have

by k_bx 6y ago

It’s not “correlation at best”. It’s an almost canonical example of the Bayesian error: given a reverse probability (if you’re sick => you’re 80% likely to have deficiency), people make a reverse conclusion (if you’re deficient => you’re 80% sick) In reality (due to Bayes theorem), we need to compute the probability of being sick when having deficiency as population_with_covid (1/47 for Spain) * 80% / population_with_deficiency. If, say, there’s 60% vitamin D deficient people in Spain, it’d give us 2% chance of getting a disease if you have deficiency. Not much!

Jugurtha 6y ago
I'd argue it's not even a Bayesian error but a logic error stemming from difficulty with contraposition.[0] It checks out even if you remove the probability aspect of it and use a simple implication. - [0]: https://en.wikipedia.org/wiki/Contraposition https://en.wikipedia.org/wiki/Contraposition
faeyanpiraat 6y ago
I believe you are wrong about what we want to calculate. It's not about whether you have a higher chance of getting infected if you are vitamin D deficient. It's about whether you need medical attention in a hostpital if you do. So if we have X people who got COVID, and out of those X people Y% needed to spend time in a hospital, and 80% of them had D vitamin deficiency, then it does not matter what is the Y% value. The important thing is that the more severe cases had D vitamin deficiency, therefore you have a higher chance to get a severe case if you are deficient. Right?
- 542354234235 6y ago
  > So if we have X people who got COVID, and out of those X people Y% needed to spend time in a hospital, and 80% of them had D vitamin deficiency, then it does not matter what is the Y% value It does matter because you need to know what the percent that didn’t need to spend time in the hospital. For instance, if 80% of the people that did not have to be hospitalized also had a Vitamin D deficiency, then there is nothing meaningful about the deficiency because it is the same between the two groups. I could say pretty confidently that 80% of people hospitalized for COVID have brown eyes. Why? Because the overall population is about 80% brown eyed. We need to look at the difference first and foremost. > The important thing is that the more severe cases had D vitamin deficiency, therefore you have a higher chance to get a severe case if you are deficient. Even if we found a large difference, that is far too little information to assume causation. For instance, it could be that the elderly are more likely to be Vitamin D deficient due to being sedentary and spending most of their time indoors, and the elderly are more likely to be hospitalized due to their age. So it wouldn’t be Vitamin D deficiency, it would be age that was the underlying cause of both phenomenon. We need to be very careful about making these leaps in logic, since it can send us down pointless rabbit holes and have people spending time and resources on things that do not actually help.
  - faeyanpiraat 6y ago
    I see. Genuine question: Do you happen to be able to estimate how many people and of which qualifications you require in a team for how long to go trough all the available research, and make some useful and fairly certain prescriptions in a complex topic like this? Is it even realistic for an average joe to look into it in their free time, and come to a useful conslusion in a realistic timeframe, or is everything so complicated nowadays that it's not worth it?
    - 542354234235 6y ago
      > Is it even realistic for an average joe to look into it in their free time, and come to a useful conslusion in a realistic timeframe, or is everything so complicated nowadays that it's not worth it? In my personal opinion, no it isn’t. I would say that it would be useful to look into how scientific and medical research is conducted, how peer review works, etc. and you will see the incredible complexity and difficulty of building up a medical theory. I’d also look at skeptic explanations of how pseudoscience uses that complexity to push things that just aren’t true. Without a deep understanding of topic, and all the underlying scientific method, you are far more likely to come to a wrong conclusion than a correct one. Finding good scientific communicators, I’ve found, is the best way to get good information. People that do have the requisite knowledge and that will contextualize the sensational and just bad reporting of science and medicine. I would suggest Science Based Medicine [1] and Heathcare Triage [2] as a start. [1] https://sciencebasedmedicine.org/ https://sciencebasedmedicine.org/ [2] https://www.youtube.com/user/thehealthcaretriage https://www.youtube.com/user/thehealthcaretriage
  - smaryjerry 6y ago
    Not sure why people think elderly stay in doors more. Elderly usually retire and spend much more time outdoors than those in the middle of life working 8 hours a day. However it is true that elderly absorb at a slower rate and someone already on their death bed and unable to walk would spend more time indoors. Those people are usually given vitamin d supplements though as when you are already sick doctors know you will be deficient and recommend vitamin D.

by k_bx 6y ago

Jugurtha 6y ago

I'd argue it's not even a Bayesian error but a logic error stemming from difficulty with contraposition.[0] It checks out even if you remove the probability aspect of it and use a simple implication. - [0]: https://en.wikipedia.org/wiki/Contraposition https://en.wikipedia.org/wiki/Contraposition

faeyanpiraat 6y ago

I believe you are wrong about what we want to calculate. It's not about whether you have a higher chance of getting infected if you are vitamin D deficient. It's about whether you need medical attention in a hostpital if you do. So if we have X people who got COVID, and out of those X people Y% needed to spend time in a hospital, and 80% of them had D vitamin deficiency, then it does not matter what is the Y% value. The important thing is that the more severe cases had D vitamin deficiency, therefore you have a higher chance to get a severe case if you are deficient. Right?

542354234235 6y ago
> So if we have X people who got COVID, and out of those X people Y% needed to spend time in a hospital, and 80% of them had D vitamin deficiency, then it does not matter what is the Y% value It does matter because you need to know what the percent that didn’t need to spend time in the hospital. For instance, if 80% of the people that did not have to be hospitalized also had a Vitamin D deficiency, then there is nothing meaningful about the deficiency because it is the same between the two groups. I could say pretty confidently that 80% of people hospitalized for COVID have brown eyes. Why? Because the overall population is about 80% brown eyed. We need to look at the difference first and foremost. > The important thing is that the more severe cases had D vitamin deficiency, therefore you have a higher chance to get a severe case if you are deficient. Even if we found a large difference, that is far too little information to assume causation. For instance, it could be that the elderly are more likely to be Vitamin D deficient due to being sedentary and spending most of their time indoors, and the elderly are more likely to be hospitalized due to their age. So it wouldn’t be Vitamin D deficiency, it would be age that was the underlying cause of both phenomenon. We need to be very careful about making these leaps in logic, since it can send us down pointless rabbit holes and have people spending time and resources on things that do not actually help.
- faeyanpiraat 6y ago
  I see. Genuine question: Do you happen to be able to estimate how many people and of which qualifications you require in a team for how long to go trough all the available research, and make some useful and fairly certain prescriptions in a complex topic like this? Is it even realistic for an average joe to look into it in their free time, and come to a useful conslusion in a realistic timeframe, or is everything so complicated nowadays that it's not worth it?
  - 542354234235 6y ago
    > Is it even realistic for an average joe to look into it in their free time, and come to a useful conslusion in a realistic timeframe, or is everything so complicated nowadays that it's not worth it? In my personal opinion, no it isn’t. I would say that it would be useful to look into how scientific and medical research is conducted, how peer review works, etc. and you will see the incredible complexity and difficulty of building up a medical theory. I’d also look at skeptic explanations of how pseudoscience uses that complexity to push things that just aren’t true. Without a deep understanding of topic, and all the underlying scientific method, you are far more likely to come to a wrong conclusion than a correct one. Finding good scientific communicators, I’ve found, is the best way to get good information. People that do have the requisite knowledge and that will contextualize the sensational and just bad reporting of science and medicine. I would suggest Science Based Medicine [1] and Heathcare Triage [2] as a start. [1] https://sciencebasedmedicine.org/ https://sciencebasedmedicine.org/ [2] https://www.youtube.com/user/thehealthcaretriage https://www.youtube.com/user/thehealthcaretriage
- smaryjerry 6y ago
  Not sure why people think elderly stay in doors more. Elderly usually retire and spend much more time outdoors than those in the middle of life working 8 hours a day. However it is true that elderly absorb at a slower rate and someone already on their death bed and unable to walk would spend more time indoors. Those people are usually given vitamin d supplements though as when you are already sick doctors know you will be deficient and recommend vitamin D.