5 ms·

> It's so strange to me that these studies seem to generalize findings (eg results by country) when one of the key biological factors for how we get vitamin D i

> It's so strange to me that these studies seem to generalize findings (eg results by country) when one of the key biological factors for how we get vitamin D is skin colour. They bypass skin color by just measuring levels of Vitamin D directly. This study doesn't care how you got the Vitamin D, it just cares how much you have. There are tons of problems with this study, but failure to look at skin color isn't one of them.

JumpCrisscross 6y ago
> They bypass skin color by just measuring levels of Vitamin D directly People with darker skin will, ceteris paribus, have lower vitamin D levels. And all else is not equal.
- kerkeslager 6y ago
  True, but irrelevant. Even if skin color is a predictor of vitamin D levels, this study doesn't need to predict vitamin D levels because they used measured vitamin D levels.
  - JumpCrisscross 6y ago
    > this study doesn't need to predict vitamin D levels because they used measured vitamin D levels If darker-skinned people have, on average, lower vitamin D levels, then measuring vitamin D levels proxies for skin color. So if the underlying cause is e.g. access to healthcare or stress or exposure to airborne particulates, and those correlate with skin color, those will also correlate with vitamin D levels. One could thus find vitamin D levels relate strongly to outcomes. But increasing vitamin D has zero effect on the outcome. Because it's not the cause. (We see this a lot with poverty correlates in education.)
    - kerkeslager 6y ago
      > If darker-skinned people have, on average, lower vitamin D levels, then measuring vitamin D levels proxies for skin color. "Proxies for" doesn't have a scientific meaning that I'm aware of, so I can't be sure that I understand what you're saying. If what you're saying is that vitamin D levels are correlated with skin color, true, but irrelevant to this study. If what you're saying is that the (poorly substantiated) correlation between Covid19 and vitamin D can be used to claim a correlation between Covid19 and skin color: no, because it's quite possible that vitamin D levels have no effect on Covid19 in people with darker skin, but a huge effect on Covid19 in people with light skin. You also have to keep in mind that your errors multiply across different correlations: the error margin of correlating Covid 19 with skin color via this method is the error margin of correlating Covid19 with vitamin D and the error margi of correlating vitamin D with skin color. If what you're saying is that the (poorly substantiated) correlation between Covid19 and vitamin D can be used to establish a causal relation between Covid 19 and skin color, no, because in addition to the previous problems, you're ignoring that there at least 10 confounding factors besides skin color which also have correlation with vitamin D levels: 1. Latitude 2. How much time you spend outside 3. Which time you spend outside 4. Clothing 5. Sunscreen 6. Liver function 7. Diet 8. Supplementation 9. Cloud cover over time 10. Season If what you're saying is that this study can be used to establish a causal relation between Covid19 and skin color: in addition to all the previous problems, this study can't even really be used to establish a correlation between vitamin D and Covid19, so do we really need to pile on more logical fallacies than are already present?
      - JumpCrisscross 6y ago
        > "Proxies for" doesn't have a scientific meaning that I'm aware of It's a term, roughly, for intermediate variables [1]. Vitamin D levels are a likely proxy for a host of race-variant socioeconomic factors. [1] https://en.wikipedia.org/wiki/Proxy_(statistics) https://en.wikipedia.org/wiki/Proxy_(statistics)
        kerkeslager 6y ago
        By the definition on that page, vitamin D isn't a proxy for skin color. > In statistics, a proxy or proxy variable is a variable that is not in itself directly relevant, but that serves in place of an unobservable or immeasurable variable. In order for a variable to be a good proxy, it must have a close correlation, not necessarily linear, with the variable of interest. This correlation might be either positive or negative. > Proxy variable must relate to unobserved variable, must correlate with disturbance, and must not correlate with regressors once disturbance is controlled for. Skin color isn't an unobservable or immeasurable variable, and it does correlate with regressors once disturbance is controlled for.
      - b1daly 6y ago
        I believe what they are saying is that if their is a correlation between skin color and vitamin D levels (people with darker skin have less vitamin D) and there is another reason people with darker skin have poor outcomes (let’s say bad healthcare), it would make any conclusion that the vitamin D levels have a causal relationship to covid-19 outcomes less likely. To account for this, you would need to control for skin color.
- zamfi 6y ago
  Huh? The authors of this (flawed) study are making the claim that Vitamin D deficiency correlates with negative outcomes from COVID-19. They are doing this by using public measures of country-wide serum-based Vitamin D deficiency rates and COVID-19 outcomes. How is "where the Vitamin D comes from" relevant at all to this particular correlation? It might be relevant if you're interested in a correlation of Vitamin D deficiency and anything having to do with the sun -- but that's not the correlation they're making here.
  - firethief 6y ago
    Say people in a neighborhood are getting cholera. Some of the residents collect rainwater, while others walk to the Broad Street well. The people who use the well are better hydrated at baseline, and you are exploring the correlation between hydration and cholera. Is where the water comes from relevant?
    - kerkeslager 6y ago
      You're struggling here because you're not being specific enough in your reading and you're not being specific enough in your writing either. Is where the water comes from relevant to what? You need to be more specific. Is where the water comes from relevant to the correlation between where the water comes from and cholera? Tautologically yes. Is where the water comes from relevant to the correlation between hydration and cholera? No. The reason you need to be more specific is that these are completely different experiments: If you want to see whether where the water comes from is correlated with cholera, you might observe everyone who goes to the well and everyone who collects rainwater for 30 days, and see whether more from the well group or more from the rainwater group develop cholera. Note: you aren't collecting any data in this experiment about how hydrated these people are. If you want to see whether hydration is correlated with cholera, you might randomly select 30 people and measure how much water they collect every day for 30 days, and plot that against whether they develop cholera. Note: you aren't collecting any data in this experiment about where these people get their water. "Is skin color correlated to vitamin D absorption from the sun?" and "Are vitamin D levels correlated with Covid19 infection and severity?" are two completely different questions and two completely different experiments. And to be clear, they aren't even connected by a common cofactor: "vitamin D absorption from the sun" and "vitamin D levels" are two very different things, which may not even be correlated in certain situations (that is to say, I may absorb very little vitamin D from the sun, yet have very high vitamin D levels--this could happen if I supplement or consume a lot of vitamin D in my diet). You cannot draw any conclusions about vitamin D absorption from the sun or skin color from this study, because it does not collect any data about those vitamin D absorption from the sun, and it does not collect any data about skin color.
- adrianmonk 6y ago
  My interpretation (which might be wrong) of the study abstract is that it is known that Vitamin D levels vary in different regions, and it's also known that COVID-19 mortality varies. And these things are the motivation to study whether Vitamin D levels have a connection to mortality. So they measured Vitamin D levels and measured mortality and looked to see if there is a correlation.
deleted 6y ago
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JumpCrisscross 6y ago

> They bypass skin color by just measuring levels of Vitamin D directly People with darker skin will, ceteris paribus, have lower vitamin D levels. And all else is not equal.

kerkeslager 6y ago
True, but irrelevant. Even if skin color is a predictor of vitamin D levels, this study doesn't need to predict vitamin D levels because they used measured vitamin D levels.
- JumpCrisscross 6y ago
  > this study doesn't need to predict vitamin D levels because they used measured vitamin D levels If darker-skinned people have, on average, lower vitamin D levels, then measuring vitamin D levels proxies for skin color. So if the underlying cause is e.g. access to healthcare or stress or exposure to airborne particulates, and those correlate with skin color, those will also correlate with vitamin D levels. One could thus find vitamin D levels relate strongly to outcomes. But increasing vitamin D has zero effect on the outcome. Because it's not the cause. (We see this a lot with poverty correlates in education.)
  - kerkeslager 6y ago
    > If darker-skinned people have, on average, lower vitamin D levels, then measuring vitamin D levels proxies for skin color. "Proxies for" doesn't have a scientific meaning that I'm aware of, so I can't be sure that I understand what you're saying. If what you're saying is that vitamin D levels are correlated with skin color, true, but irrelevant to this study. If what you're saying is that the (poorly substantiated) correlation between Covid19 and vitamin D can be used to claim a correlation between Covid19 and skin color: no, because it's quite possible that vitamin D levels have no effect on Covid19 in people with darker skin, but a huge effect on Covid19 in people with light skin. You also have to keep in mind that your errors multiply across different correlations: the error margin of correlating Covid 19 with skin color via this method is the error margin of correlating Covid19 with vitamin D and the error margi of correlating vitamin D with skin color. If what you're saying is that the (poorly substantiated) correlation between Covid19 and vitamin D can be used to establish a causal relation between Covid 19 and skin color, no, because in addition to the previous problems, you're ignoring that there at least 10 confounding factors besides skin color which also have correlation with vitamin D levels: 1. Latitude 2. How much time you spend outside 3. Which time you spend outside 4. Clothing 5. Sunscreen 6. Liver function 7. Diet 8. Supplementation 9. Cloud cover over time 10. Season If what you're saying is that this study can be used to establish a causal relation between Covid19 and skin color: in addition to all the previous problems, this study can't even really be used to establish a correlation between vitamin D and Covid19, so do we really need to pile on more logical fallacies than are already present?
    - JumpCrisscross 6y ago
      > "Proxies for" doesn't have a scientific meaning that I'm aware of It's a term, roughly, for intermediate variables [1]. Vitamin D levels are a likely proxy for a host of race-variant socioeconomic factors. [1] https://en.wikipedia.org/wiki/Proxy_(statistics) https://en.wikipedia.org/wiki/Proxy_(statistics)
      - kerkeslager 6y ago
        By the definition on that page, vitamin D isn't a proxy for skin color. > In statistics, a proxy or proxy variable is a variable that is not in itself directly relevant, but that serves in place of an unobservable or immeasurable variable. In order for a variable to be a good proxy, it must have a close correlation, not necessarily linear, with the variable of interest. This correlation might be either positive or negative. > Proxy variable must relate to unobserved variable, must correlate with disturbance, and must not correlate with regressors once disturbance is controlled for. Skin color isn't an unobservable or immeasurable variable, and it does correlate with regressors once disturbance is controlled for.
    - b1daly 6y ago
      I believe what they are saying is that if their is a correlation between skin color and vitamin D levels (people with darker skin have less vitamin D) and there is another reason people with darker skin have poor outcomes (let’s say bad healthcare), it would make any conclusion that the vitamin D levels have a causal relationship to covid-19 outcomes less likely. To account for this, you would need to control for skin color.
zamfi 6y ago
Huh? The authors of this (flawed) study are making the claim that Vitamin D deficiency correlates with negative outcomes from COVID-19. They are doing this by using public measures of country-wide serum-based Vitamin D deficiency rates and COVID-19 outcomes. How is "where the Vitamin D comes from" relevant at all to this particular correlation? It might be relevant if you're interested in a correlation of Vitamin D deficiency and anything having to do with the sun -- but that's not the correlation they're making here.
- firethief 6y ago
  Say people in a neighborhood are getting cholera. Some of the residents collect rainwater, while others walk to the Broad Street well. The people who use the well are better hydrated at baseline, and you are exploring the correlation between hydration and cholera. Is where the water comes from relevant?
  - kerkeslager 6y ago
    You're struggling here because you're not being specific enough in your reading and you're not being specific enough in your writing either. Is where the water comes from relevant to what? You need to be more specific. Is where the water comes from relevant to the correlation between where the water comes from and cholera? Tautologically yes. Is where the water comes from relevant to the correlation between hydration and cholera? No. The reason you need to be more specific is that these are completely different experiments: If you want to see whether where the water comes from is correlated with cholera, you might observe everyone who goes to the well and everyone who collects rainwater for 30 days, and see whether more from the well group or more from the rainwater group develop cholera. Note: you aren't collecting any data in this experiment about how hydrated these people are. If you want to see whether hydration is correlated with cholera, you might randomly select 30 people and measure how much water they collect every day for 30 days, and plot that against whether they develop cholera. Note: you aren't collecting any data in this experiment about where these people get their water. "Is skin color correlated to vitamin D absorption from the sun?" and "Are vitamin D levels correlated with Covid19 infection and severity?" are two completely different questions and two completely different experiments. And to be clear, they aren't even connected by a common cofactor: "vitamin D absorption from the sun" and "vitamin D levels" are two very different things, which may not even be correlated in certain situations (that is to say, I may absorb very little vitamin D from the sun, yet have very high vitamin D levels--this could happen if I supplement or consume a lot of vitamin D in my diet). You cannot draw any conclusions about vitamin D absorption from the sun or skin color from this study, because it does not collect any data about those vitamin D absorption from the sun, and it does not collect any data about skin color.
adrianmonk 6y ago
My interpretation (which might be wrong) of the study abstract is that it is known that Vitamin D levels vary in different regions, and it's also known that COVID-19 mortality varies. And these things are the motivation to study whether Vitamin D levels have a connection to mortality. So they measured Vitamin D levels and measured mortality and looked to see if there is a correlation.

deleted 6y ago

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