4 ms·

> It does mean that the particular causal link in question is marginally more likely than if the correlation had not been observed. Not really -- it fails to c

by lutusp 13y ago

> It does mean that the particular causal link in question is marginally more likely than if the correlation had not been observed. Not really -- it fails to consider the possibility that B caused A rather than the reverse, or that an unevaluated cause C caused both A and B. This is why I hate hearing the common phrase, "In a recent study, (something) has been linked to (something)". The words aren't false, but they're misleading to an untrained person. > That again, though, doesn't really tell us enough to be useful. That's certainly true.

dllthomas 13y ago
"Not really -- it fails to consider the possibility that B caused A rather than the reverse, or that an unevaluated cause C caused both A and B." Yes really! Just because things are uncertain doesn't mean they're equally uncertain as you learn new facts! "A causes B" doesn't become more likely relative to "B causes A" when you learn there is a correlation, but both become more likely relative to "there is no causal relationship between A and B whatsoever" and thus more likely overall. Probabilities sum to 100%. We learned that one possibility is less likely - that probability has to go somewhere.
- lutusp 13y ago
  > Just because things are uncertain doesn't mean they're equally uncertain as you learn new facts! But that's the foundation on which science is built -- the null hypothesis -- the default precept that a correlation has no meaning without evidence supporting one. The idea that unexplained correlations are assumed to arise from chance, not an uncovered cause. Until there's evidence that cannot be explained any other way, two apparently connected things are presumed to be connected by chance. > ... but both become more likely relative to "there is no causal relationship between A and B whatsoever" You're starting out making an assumption that has no basis. In science, the default assumption about a correlation is that it has no meaning whatsoever. > Probabilities sum to 100%. Yes, they do, but the initial probability is 100% that the correlation arises from chance. This is why the scientists at the LHC refused to speculate about the existence of the Higgs until they had acquired a p factor of 5σ. Details: http://blogs.scientificamerican.com/observations/2012/07/17/five-sigmawhats-that/ http://blogs.scientificamerican.com/observations/2012/07/17/... "Scientists use p-values to test the likelihood of hypotheses. In an experiment comparing some phenomenon A to phenomenon B, researchers construct two hypotheses: that “A and B are not correlated,” which is known as the null hypothesis, and that “A and B are correlated,” which is known as the research hypothesis." "The researchers then assume the null hypothesis (because it’s the most conservative supposition, intellectually) and calculate the probability of obtaining data as extreme or more extreme than what they observed, given that there is no relationship between A and B. This calculation, which yields the p-value, can be based on any of several different statistical tests. If the p-value is low, for example 0.01, this means that there is only a small chance (one percent for p=0.01) that the data would have been observed by chance without the correlation. Usually there is a pre-established threshold in a field of study for rejecting the null hypothesis and claiming that A and B are correlated. Values of p=0.05 and p=0.01 are very common in many scientific disciplines."
  - dllthomas 13y ago
    "Yes, they do, but the initial probability is 100% that the correlation arises from chance." If you believe that's true, I've got some wagers I'd like to make with you. You don't mind zillion-to-one odds, right?
    - lutusp 13y ago
      Wagers and science are opposite endeavors. A scientist must not care how his theory turns out, but a gambler must care.
      - dllthomas 13y ago
        They're different, but they're not opposite. Both involve probability and statistics. And those of us trying to make decisions in the real world must care how our decisions are likely to turn out. Edited to add: More to the point, does the universe care if you're a scientist or a gambler and change the laws of probability? Presuming the answer is no, pretend you're a gambler for a minute, and you should see what's wrong with statement "the initial probability is 100% that the correlation arises from chance": I offer you a wager, where we pick a correlation about which you have not formulated a hypothesis, and if I can show causation of any sort you give me zillions of dollars; if I can't, I give you a dollar. Your expected value, with an assumption of 100%, is that you always get the dollar. Do you really think that, over zillions of games, you'd make money? Edited again: The hypothetical people you're criticizing - who read this article and go out to find a man - aren't trying to "do science", they're trying to successfully wager and make the best bet they can with their health and their life. Of course, we agree that if they're making substantial changes based on this study, they're probably wagering poorly, but that's beside the point.
        lutusp 13y ago
        > And those of us trying to make decisions in the real world must care how our decisions are likely to turn out. Yes -- unless you're a scientist. If you're a scientist and you expect to make a contribution to the store of human knowledge, you cannot care one way or another how your experiments turn out, only that they're conducted with the maximum amount of dispassion and objectivity. > The hypothetical people you're criticizing - who read this article and go out to find a man - aren't trying to "do science", they're trying to successfully wager ... Yes, which is why we see so many articles like the one this thread discusses -- articles that cynically harvest human stupidity to some unworthy purpose.

by lutusp 13y ago

dllthomas 13y ago

"Not really -- it fails to consider the possibility that B caused A rather than the reverse, or that an unevaluated cause C caused both A and B." Yes really! Just because things are uncertain doesn't mean they're equally uncertain as you learn new facts! "A causes B" doesn't become more likely relative to "B causes A" when you learn there is a correlation, but both become more likely relative to "there is no causal relationship between A and B whatsoever" and thus more likely overall. Probabilities sum to 100%. We learned that one possibility is less likely - that probability has to go somewhere.

lutusp 13y ago
> Just because things are uncertain doesn't mean they're equally uncertain as you learn new facts! But that's the foundation on which science is built -- the null hypothesis -- the default precept that a correlation has no meaning without evidence supporting one. The idea that unexplained correlations are assumed to arise from chance, not an uncovered cause. Until there's evidence that cannot be explained any other way, two apparently connected things are presumed to be connected by chance. > ... but both become more likely relative to "there is no causal relationship between A and B whatsoever" You're starting out making an assumption that has no basis. In science, the default assumption about a correlation is that it has no meaning whatsoever. > Probabilities sum to 100%. Yes, they do, but the initial probability is 100% that the correlation arises from chance. This is why the scientists at the LHC refused to speculate about the existence of the Higgs until they had acquired a p factor of 5σ. Details: http://blogs.scientificamerican.com/observations/2012/07/17/five-sigmawhats-that/ http://blogs.scientificamerican.com/observations/2012/07/17/... "Scientists use p-values to test the likelihood of hypotheses. In an experiment comparing some phenomenon A to phenomenon B, researchers construct two hypotheses: that “A and B are not correlated,” which is known as the null hypothesis, and that “A and B are correlated,” which is known as the research hypothesis." "The researchers then assume the null hypothesis (because it’s the most conservative supposition, intellectually) and calculate the probability of obtaining data as extreme or more extreme than what they observed, given that there is no relationship between A and B. This calculation, which yields the p-value, can be based on any of several different statistical tests. If the p-value is low, for example 0.01, this means that there is only a small chance (one percent for p=0.01) that the data would have been observed by chance without the correlation. Usually there is a pre-established threshold in a field of study for rejecting the null hypothesis and claiming that A and B are correlated. Values of p=0.05 and p=0.01 are very common in many scientific disciplines."
- dllthomas 13y ago
  "Yes, they do, but the initial probability is 100% that the correlation arises from chance." If you believe that's true, I've got some wagers I'd like to make with you. You don't mind zillion-to-one odds, right?
  - lutusp 13y ago
    Wagers and science are opposite endeavors. A scientist must not care how his theory turns out, but a gambler must care.
    - dllthomas 13y ago
      They're different, but they're not opposite. Both involve probability and statistics. And those of us trying to make decisions in the real world must care how our decisions are likely to turn out. Edited to add: More to the point, does the universe care if you're a scientist or a gambler and change the laws of probability? Presuming the answer is no, pretend you're a gambler for a minute, and you should see what's wrong with statement "the initial probability is 100% that the correlation arises from chance": I offer you a wager, where we pick a correlation about which you have not formulated a hypothesis, and if I can show causation of any sort you give me zillions of dollars; if I can't, I give you a dollar. Your expected value, with an assumption of 100%, is that you always get the dollar. Do you really think that, over zillions of games, you'd make money? Edited again: The hypothetical people you're criticizing - who read this article and go out to find a man - aren't trying to "do science", they're trying to successfully wager and make the best bet they can with their health and their life. Of course, we agree that if they're making substantial changes based on this study, they're probably wagering poorly, but that's beside the point.
      - lutusp 13y ago
        > And those of us trying to make decisions in the real world must care how our decisions are likely to turn out. Yes -- unless you're a scientist. If you're a scientist and you expect to make a contribution to the store of human knowledge, you cannot care one way or another how your experiments turn out, only that they're conducted with the maximum amount of dispassion and objectivity. > The hypothetical people you're criticizing - who read this article and go out to find a man - aren't trying to "do science", they're trying to successfully wager ... Yes, which is why we see so many articles like the one this thread discusses -- articles that cynically harvest human stupidity to some unworthy purpose.