If you remember anything from statistics class, it's probably that correlation ain't no causation. Just because two numbers happen to go up at the same time doesn't mean that one is causing the other to rise (or fall, or hold steady, or whatever). If there isn't a plausible explanation for how the two might be connected, and proof that that explanation is indeed the cause, all you have is a couple of lines on a chart. So it's a move in the right direction when people try to suss out connections between two variables they have a hunch are related. But seeking such a connection can lead to some pretty convoluted reasoning. A new paper---unpublished, but released for discussion
---claims that the passage of states' medical marijuana laws cause decreased traffic fatalities, following on the researchers' intuition that people might smoke pot instead of drinking alcohol if marijuana were more ...
