On 14 Jan 2015, at 16:51, Jason Resch wrote:
On Wed, Jan 14, 2015 at 9:22 AM, Quentin Anciaux
<[email protected]> wrote:
2015-01-14 16:16 GMT+01:00 Jason Resch <[email protected]>:
On Wed, Jan 14, 2015 at 9:02 AM, Quentin Anciaux
<[email protected]> wrote:
2015-01-14 15:39 GMT+01:00 Jason Resch <[email protected]>:
Correlations don't prove causal relations,
I know all I point out, is that there are now many study done on
that correlation... You can dismiss them..
My point is that correlations themselves (even when proven) are
effectively meaningless. Take the supposed evidence that
nutritionists used to demonize fat as leading to heart attacks.
Correlations where shown between various countries that showed
countries with higher fat intake had higher incidence of heart
disease. But it was later shown that fat intake in countries was
determined largely by the countries per capita GDP. So now you can
see the correlational study (which put the blame on fat) could be
explained by anything else that correlates with per capita GDP:
stress, long working house, consumption of sugar, cigarette use, etc.
Think of it this way: if heart attacks correlate with economic
development of a country, another study might have been able to show
a strong correlation between driving cars and heart attacks (because
more cars are owned and more people drive in those countries). But
it would have almost certainly been wrong to conclude "Drive less to
avoid heart disease". Yet this is the same error that led
nutritionists to the bad advice of "Eat less fat to avoid heart
disease". Only a controlled study which actually tests the
hypothesis can separate mere correlations and true causes. Do we
know if cannabis correlates with depression because depressed people
seek it to self-medicate? We might observe a similar correlation
between depression and SSRI use, but we know SSRIs are used to treat
depression, so it makes sense. We don't conclude though that SSRIs
cause depression.
If your claim is that cannabis causes depression, you need to point
to a study that takes two groups of subjects, subjects one group's
members to regular cannabis use and another that prohibits cannabis
use among members, and then study whether the incidence of
depression is higher in one group vs. the other. All science is
based on "Observe, Form Theory, Test Theory". It's important that we
realize all correlation studies (in all domains) are nothing but the
first step "Observe". Forming policies or opinions from formed
theories that haven't been tested is asking for trouble. (Just look
at the current US and now world health crisis due to moving people
to low-fat diets when the only basis was a correlational study
(since disproved by controlled testing)).
yet they exists and they seems correctly done... maybe it's
prohibitionist agenda.. I know for myself that I can't control my
cannabis usage and when I was using, I was abusing and that
certainly did not help me at that time... But if you think cannabis
abuse is a fairy tale... fine with me... and if you think it is not,
but it has absolutely no side effect... ok... I won't agree with you
but it's your belief... and I've mine.
I don't see where are you getting this from out of what I said.
I'm getting at that you don't know the various studies, but you know
they are bad, and only point out correlation without anything
else... well, you can be bad faith and absolutely sure cannabis is
absolutely safe... ok then... but can I ask you studies that shows
that too ?
I said nothing either for or against cannabis use. I only cautioned
that correlational studies cannot be used to draw conclusions ever,
in any domain of inquriy. That's the only point I wanted to make.
(I'll retreat back into the dark now)
I am not sure we agree here. In inferring the local reality, we have
only correlation, and the point is only in using the statistics rightly.
When people see that 98% of the heroine user have begin with cannabis,
they draw the conclusion that cannabis leads to heroine.
That is is wrong. But if they would have shown that 98% of cannabis
user take heroin, then their argument would be used correctly to infer
a "causal relation",( not to prove it, nor to explain it at a
different level, itself based on inference taken from correlation, but
always taken in the right direction).
We cannot prove any causal relationships, but we can infer the
plausible one from data read in the good direction. Propaganda usually
take them in the wrong direction. It is a confusion between "A
included in B" and "B includes in A".
The use of correlation are never proofs or causal relationship. That
is one thing.
But only correlation can be used to infer plausible relationships, but
then they must be used in the right direction. That is another thing.
criticizing the use correlation in both directions, concerns the
truth, but not the plausiblity. It could hides the more frequent
confusion of direction in the inference of a plausible causal
relationship. I guess you are OK with this. I just want to insist as
the "wrong direction" use of correlations continue all the time.
Bruno
Jason
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