
Finding cannabinoids in hair does not prove cannabis consumption - calebgarling
http://www.nature.com/articles/srep14906
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OopsCriticality
Of note, this paper is based on data from only two volunteers (a third was
used to exclude THCA-A as a cofound).

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stevenae
It's concerning that such a low sample was published in Nature. One can
imagine a similarly underpowered study showing that a direct injection of HIV
does not cause seroconversion, because the two or three samples happened to
have CCR5-D32.

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detaro
Admittedly the sample is extremely small, but your example doesn't match what
they discuss. The claim "X does not cause Y (under any circumstances)" takes a
lot more samples to be convincing than "X is not a reliable indicator of Y
because it has false-positives", where a few examples of such false-positives
already support their existence very well.

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TrevorJ
I think it's still interesting because the common assumption is that it
shouldn't be possible at all. If you drop one apple you expect it to fall. If
it doesn't _then_ it's time to up your sample size and do further testing.

