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This article cites research that goes way beyond the usual sort of correlation. How much stronger would the evidence need to get?

by gruseom 14y ago

greendestiny 14y ago
I'm not sure, how strong should such a correlation be to be considered evidence? That's the real question. And I think when it comes to annual averages of broad trends its a real question how we should interpret correlations. To me this article is data porn, its a story with data. It may be some part of the truth, but I think it exists to entertain the data literate - so we can follow along with the numbers and pat ourselves on the back for a fact discovered. Its enough analysis to be dangerous. And in case hackernews has become so infected with the kind of reddit thinking that can only see in black and white - yes I think reducing lead in gasoline is a very good thing.
- jforman 14y ago
  The strength of the correlation or its time-scale have no bearing on whether the correlation should be considered evidence of causation. The fatal flaw of a correlation is that it can be specious — it can appear to explain reality, but really there's a third variable responsible for driving the phenomenon you're interested in. In this case, lead exposure and crime rate are correlated, but maybe lead doesn't cause crime at all: maybe something else causes crime that also happens to correlate with lead exposure. Who knows, maybe a certain pesticide was used at the same time that lead gasoline came into vogue, and that's really the true cause of the rise in crime rates. In research like this, when you can't do a manually controlled experiment, you have to control for hidden variables by some other means. And that's precisely what the investigators in this article did: they varied the input data to try to "shake out" other variables that might be behind the correlation. They looked at different time scales, different geographies, and different demographics, in an attempt to control for hidden variables that might be related to any one of those things. Every time you vary the input data and keep finding a correlation, your evidence of a causative relationship goes up. The gold standard, of course, would be to expose two random, double-blind sets of infants to lead and to a control substance and see what happens. But since that would be unethical (as we have reason to think lead is bad for you), we're stuck with animal studies or retrospective studies. Personally, I find the evidence in this article impressive, but it would take quite a lot of looking into their specific methods to come to any real conclusion.
  - greendestiny 14y ago
    That's the high level view of the problem of correlation and causation. What I'm really saying is how unlikely should we consider these correlations - especially correlations over very broad average trends in human behaviour. Now I'm sure there are some statistical tools that would give some sense of how surprising the correlation of these trends is but I'd like to know out of all the things about human society we track how many of them correlate and how closely.
    - nitrogen 14y ago
      Presumably one can correlate lead exposure with reduced intelligence independent of time.
  - SideburnsOfDoom 14y ago
    > The fatal flaw of a correlation is that it can be specious — it can appear to explain reality, but really there's a third variable responsible for driving the phenomenon you're interested in. But in the case of lead, the causal chain from lead exposure to worse behaviour is fairly well understood.
- sliverstorm 14y ago
  Would you at least agree the correlation seems strong enough to warrant further investigation?
  - greendestiny 14y ago
    Sure, it might even be strong evidence. It's just not clear and we see these time series correlations again and again.
smsm42 14y ago
Well, for starters to prove casuation one doesn't only need to show X moves in sync with Y. One also needs to show that it is not because both X and Y are caused by some reason Z which influences both even though X and Y are completely independent from each other. E.g. correlation between good lead data and good crime data may be caused by the fact that in cities with better law enforcement both criminal laws and environmental laws are enforced strictly, or because richer folks drive less polluting cars and commit less crimes. It does not mean less lead pollution causes people to be rich. The whole thing sound like classic fitting the preconceived conclusion. But there's also something like this: >>>> Not only does lead promote apoptosis, or cell death, in the brain, but the element is also chemically similar to calcium. How lead is chemically similar to calcium? They are on opposite ends of the periodic table and have very different chemical properties. That, of course, does not prevent lead from messing with ion channels, but saying lead is chemically similar to calcium is wrong.
- pixl97 14y ago
  How lead is chemically similar to calcium? They are on opposite... Then you go on to explain how lead is like calcium in its bioavailability, so in relation to the operations of a human body, lead is chemically similar to calcium (only dangerous). http://brain.oxfordjournals.org/content/126/1/5.full http://brain.oxfordjournals.org/content/126/1/5.full For example, lead’s ability to pass through the blood–brain barrier (BBB) is due in large part to its ability to substitute for calcium ions (Ca2+)
  - smsm42 14y ago
    "Ability to replace calcium in certain biochemical processes" is not nearly the same as "chemically similar to calcium". It's like saying if I stole your login for facebook I would look like you and nobody would be able to distinguish between us without DNA test. Completely different things. Biochemical processes are known for accepting a lot of substitutes, that's how a lot of drugs work. That does not mean all those are chemically similar in general - they just play similar roles in certain processes.
- gruseom 14y ago

This article cites research that goes way beyond the usual sort of correlation. How much stronger would the evidence need to get?

by gruseom 14y ago

This article cites research that goes way beyond the usual sort of correlation. How much stronger would the evidence need to get?

greendestiny 14y ago

I'm not sure, how strong should such a correlation be to be considered evidence? That's the real question. And I think when it comes to annual averages of broad trends its a real question how we should interpret correlations. To me this article is data porn, its a story with data. It may be some part of the truth, but I think it exists to entertain the data literate - so we can follow along with the numbers and pat ourselves on the back for a fact discovered. Its enough analysis to be dangerous. And in case hackernews has become so infected with the kind of reddit thinking that can only see in black and white - yes I think reducing lead in gasoline is a very good thing.

jforman 14y ago
The strength of the correlation or its time-scale have no bearing on whether the correlation should be considered evidence of causation. The fatal flaw of a correlation is that it can be specious — it can appear to explain reality, but really there's a third variable responsible for driving the phenomenon you're interested in. In this case, lead exposure and crime rate are correlated, but maybe lead doesn't cause crime at all: maybe something else causes crime that also happens to correlate with lead exposure. Who knows, maybe a certain pesticide was used at the same time that lead gasoline came into vogue, and that's really the true cause of the rise in crime rates. In research like this, when you can't do a manually controlled experiment, you have to control for hidden variables by some other means. And that's precisely what the investigators in this article did: they varied the input data to try to "shake out" other variables that might be behind the correlation. They looked at different time scales, different geographies, and different demographics, in an attempt to control for hidden variables that might be related to any one of those things. Every time you vary the input data and keep finding a correlation, your evidence of a causative relationship goes up. The gold standard, of course, would be to expose two random, double-blind sets of infants to lead and to a control substance and see what happens. But since that would be unethical (as we have reason to think lead is bad for you), we're stuck with animal studies or retrospective studies. Personally, I find the evidence in this article impressive, but it would take quite a lot of looking into their specific methods to come to any real conclusion.
- greendestiny 14y ago
  That's the high level view of the problem of correlation and causation. What I'm really saying is how unlikely should we consider these correlations - especially correlations over very broad average trends in human behaviour. Now I'm sure there are some statistical tools that would give some sense of how surprising the correlation of these trends is but I'd like to know out of all the things about human society we track how many of them correlate and how closely.
  - nitrogen 14y ago
    Presumably one can correlate lead exposure with reduced intelligence independent of time.
- SideburnsOfDoom 14y ago
  > The fatal flaw of a correlation is that it can be specious — it can appear to explain reality, but really there's a third variable responsible for driving the phenomenon you're interested in. But in the case of lead, the causal chain from lead exposure to worse behaviour is fairly well understood.
sliverstorm 14y ago
Would you at least agree the correlation seems strong enough to warrant further investigation?
- greendestiny 14y ago
  Sure, it might even be strong evidence. It's just not clear and we see these time series correlations again and again.

smsm42 14y ago

Well, for starters to prove casuation one doesn't only need to show X moves in sync with Y. One also needs to show that it is not because both X and Y are caused by some reason Z which influences both even though X and Y are completely independent from each other. E.g. correlation between good lead data and good crime data may be caused by the fact that in cities with better law enforcement both criminal laws and environmental laws are enforced strictly, or because richer folks drive less polluting cars and commit less crimes. It does not mean less lead pollution causes people to be rich. The whole thing sound like classic fitting the preconceived conclusion. But there's also something like this: >>>> Not only does lead promote apoptosis, or cell death, in the brain, but the element is also chemically similar to calcium. How lead is chemically similar to calcium? They are on opposite ends of the periodic table and have very different chemical properties. That, of course, does not prevent lead from messing with ion channels, but saying lead is chemically similar to calcium is wrong.

pixl97 14y ago
How lead is chemically similar to calcium? They are on opposite... Then you go on to explain how lead is like calcium in its bioavailability, so in relation to the operations of a human body, lead is chemically similar to calcium (only dangerous). http://brain.oxfordjournals.org/content/126/1/5.full http://brain.oxfordjournals.org/content/126/1/5.full For example, lead’s ability to pass through the blood–brain barrier (BBB) is due in large part to its ability to substitute for calcium ions (Ca2+)
- smsm42 14y ago
  "Ability to replace calcium in certain biochemical processes" is not nearly the same as "chemically similar to calcium". It's like saying if I stole your login for facebook I would look like you and nobody would be able to distinguish between us without DNA test. Completely different things. Biochemical processes are known for accepting a lot of substitutes, that's how a lot of drugs work. That does not mean all those are chemically similar in general - they just play similar roles in certain processes.
gruseom 14y ago