A personal weed versus tobacco experience

I just realized something about my family. My grandmother has smoked tobacco all her life, but never weed - and her sister, my great aunt, has smoked weed all her life but not tobacco. My grandmother, who smokes cigarettes, has gotten breast cancer twice, and has emphysema, while my great aunt has never had a single problem with cancer or her lungs. The reason I bring this up is they are both females, with roughly the same physical structure, reasonably close age, and of the same geneology.

So while not entirely conclusive, I'm gonna call bullshit once again on the 1 joint = x number of cigarettes myth.