Anecdotally, I was diagnosed with asthma as a child and walked around with an inhaler for a few years. I liked it, it tasted funny and seemed like a cool gadget at the time. But I did not have asthma. And I'm convinced there's no way my parents would've been diagnosed with it 30 years ago with the minor symptoms I had.

So perhaps the asthma numbers are influenced by an increased willingness to diagnose it. Just a thought.

Auto immune diseases as a whole have increased over just the past 30 years; I'd speculate asthma is a part of this.

It will be interesting to see the driving environmental causalities behind these autoimmune disease increases if pollution is not a key variable.

Outdoor air quality isn't the only factor in developing asthma

I feel that mere causation is sufficient to promote action. Waiting for causation feels like rationalizing laziness.

People don't wait to determine whether school district performance is caused by the staff or the selection effect of eager parents, they just move to good school districts.

Chase those good effects AND attempt to understand them. Understanding the mechanism is not necessary to select for good results.

(All ethics is utilitarian in effect. Kantians stop pretending.)

About 20 years ago our society gained a deep understanding of the notion of causality. (To learn more, search the web for "Judea Pearl".) According to the terminology standardized at that time, yes, if adding particulate pollution to the air makes it more likely that a person breathing that air is depressed, then that is a casual link or a cause-and-effect relationship. It might be the case however that polluting the air reduces the person's quality of life and that if it were possible to effect an identical reduction of quality of life without polluting the air, then polluting the air would have no further effect on the likelihood of depression. if that is the case, we say that quality of life "screens off" the effect of air pollution on depression.