Coincidentally, I just read an hour ago a nice essay on correlation and causation, specifically in the context of the OPs question, smoking and cancer. It gives some sense of the evidence, and some thoughts on the continuum between correlation and causation.
I don’t think you can establish causation the way you can correlation. When they say “correlation does not imply causation” what they neglect to mention is that nothing else does either. Correlation is a fact – a statistical measure of the similarity between two data sets. Causation is something you posit. You create a theory (which doesn’t mean “guess” – but does mean “a model used to describe our understanding of how the world works, our confidence in which is determined by how closely the model’s predictions correspond to experiment”), and the theory tells you what causes what, and ideally how and by what mechanism it causes it. And I don’t think we have a good theory yet about what causes cancer.
That doesn’t mean that a high correlation between smoking and cancer isn’t a good reason to quit. Hell, anyone who smokes more than casually and infrequently can tell you how bad it is for their health, long before they’re close to getting cancer. Even if it turns out cigarettes don’t cause cancer (and I wouldn’t bet on that), there are a million other reasons to quit.
Did any of those look at pack-a-day smokers of cannabis? If nothing else, typical use of marijuana is going to be less carcinogenic than typical use of tobacco just because the quantities are so much lower. Besides which, I never said that the risks were the same for all smoked substances, just that they’re there.
[QUOTE=DrCube;18323967And I don’t think we have a good theory yet about what causes cancer.[/QUOTE]
Erm, in a nutsheull, DNA damage of an individual cell screws up several mechanisms controlling how it grows and divides, and it grows into a tumor. Once you have a population of fast-dividing cells, there’s selective pressure for more aggressive cells that divide even faster and invade other parts of the body.
Maybe I’m misunderstanding what you meant by that statement?
I know of one study conducted on a group of rasta-level weed smokers. The doctor conducting the study specifically chose subjects who did not smoke tobacco, but did smoke high levels of cannabis daily. After the study concluded, he expressed surprise at the results. He expected to find some of the same health effects as cigarette smokers, such as cancer, emphysema, and associated respiratory disorders.
He found evidence of none of these things in the chronic dope smokers. He even noticed that some of them seemed to improve in some areas.
There may be others. If you’re really interested, I’ll see if I can dig up the details on the study and the doctor.
[QUOTE=lazybratsche]
Maybe I’m misunderstanding what you meant by that statement?
[/QUOTE]
How does smoke cause DNA damage?