What percentage would it be?

Question

It is estimated that smoking can cause 85% of the lung cancer.  If there were 186,516 new cases last year.  How many cases could have been avoided by not smoking?

Answer 1

That depends on what your first statement means.  Does it mean that 85% of all new cancer cases were caused by smoking?  Then multiply .85 times 186,516.

 

Or, does it mean that, among smokers, 85% of the cancer cases were caused by smoking?  Then you can't answer the question, because the 186K number isn't broken out by smoker/nonsmoker.

 

Googling, the 85% seems to be of lung cancer deaths, rather than lung cancer cases, but it's not too far out of line to assume that cases are roughly proportional to deaths.