Charles Davis Jul 17, 2016:

@Clark_NVG This crucially important new context makes it clear that they are using "incidence" to mean incidence of asthma attacks, not (as it normally means in epidemiology) incidence of contracting asthma.

Nevertheless, it remains the case that "incidence" and "risk" are not synonyms.

Nam Vo (asker) Jul 17, 2016:

New related context: Illustrating this, researchers from Britain’s Imperial College (Shaheen et al.
2008) studied the association between acetaminophen use and asthma incidence among 1,028 asthmatics and healthy matched controls.
They found that the weekly use of acetaminophen was significantly related to a diagnosis of asthma.
The researchers concluded that:
“These data add to the increasing and consistent epidemiological evidence implicating frequent paracetamol [acetaminophen] use in asthma in diverse populations.”

Note: Please focus on the bold text!
If the incidence of asthma is the number of people that contract it in this case, then the word "asthmatics" should not exist, I think.

Nam Vo (asker) Jul 13, 2016:

Thank you guys for your amazing support! I appreciate it!
Thanks, Charles for your clear explanation!

Charles Davis Jul 13, 2016:

Not redundant if terms being used correctly "Incidence" means the number of new cases of a condition, here asthma, in a specific population in a given period. You discover incidence by studying a population and counting cases of the condition. Incidence, in itself, says nothing about why these cases arise. I would be surprised if the author were using the term "incidence" in any other sense. If the author meant number of attacks, they would have said so.

"Risk", as has been said, is probability of a given individual or group of individuals developing asthma. Risk is all about causes; you compare those who share a certain feature (e.g. diet) with those who don't. Again, it is very unlikely that the author means risk of those diagnosed with asthma suffering an attack; it should and almost certainly does refer to risk of developing asthma, becoming a new case.

Other things being equal, increased/decreased risk for a given part of the population logically translates into increased/decreased incidence in the population at large. But other things often aren't equal, we don't know how many people are affected by this risk factor or other risk factors, and in any case risk is not certainty.

Terry Richards Jul 13, 2016:

It is redundant (or not)! It really depends on what the author means by "incidence". If they mean the number of attacks that an asthma suffer has, then it is not redundant. The two clauses are independent.

However, if they mean the number of people that have asthma, it is redundant. The risk is calculated from the number of sufferers divided by the total population. As total population is a constant (at any point in time), risk and incidence are directly related and are just two different ways of expressing the same thing.