The headline writer tells us "Cold cuts could cause cancer: study". This is typical of all such headlines, and it always is frustrating because without fail, these studies make claims that are much more specific. Therefore, we must read the articles carefully, and also ask clarifying questions.
Start with: All cold cuts, or only certain types of cold cuts? Any kind of cancer or a specific type of cancer?
The reporter tells us the researchers found a "positive nonlinear association between red meat cold cuts and bladder cancer," which is a very different thing from "cold cuts cause cancer". Besides, they found no association between beef, hamburger, steak, sausage or bacon and bladder cancer.
Next: What patients? Male/female? Age?
Answer: men and women aged 50-71, in eight US states. The article did not state which states.
Statistical thinkers would also wonder about this statement:
The scientists also found that people who ate the most red meat were younger, less educated, less physically active, and had lower dietary intake of fruits, vegetable, and vitamins C and E than those consuming the least red meat.
Once the cause of a disease is found, it is natural to ask the question which types of people are most at-risk, and in this case, it is natural to ask who eats the most red meat cold cuts.
However, the fact that those who eat the most red meat cold cuts also eat less fruits, vegetables, etc., and are less educated, and so on, should raise profound questions about what is the real cause of the bladder cancer! Did the researchers rule out lower consumption of fruits and vegetables (say) as a cause for increased bladder-cancer risk? (The subject of causal models is covered in Chapter 2.)
(Also, we should not tolerate the sloppiness in the language used in this (and similar) article: every time they mention "red meat", we should be reading "red meat cold cuts", and they are not the same things!)