Evenly divide all people into two groups, and apply higher taxes to one group.
Best of luck getting that one to fly in practice.
Changing taxes for everyone fails to test for a common cause of tax changes and smoking.
That’s the general problem with instrumental variables. But sometimes that’s all you have to work with.
Deterministic cause and effect is easy to test. Stochastic cause and effect, much less so, especially with unknown confounding factors.
That is the fundamental problem of statistical experiments.
Well, it’s just as easy as varying smoking directly, which would also work to identify a smoking->cancer effect.
Without experimentation, there is no way to distinguish between the world of smoker’s lesion and the world of carcinogenic cigarettes.
Best of luck getting that one to fly in practice.
That’s the general problem with instrumental variables. But sometimes that’s all you have to work with.
That is the fundamental problem of statistical experiments.
Well, it’s just as easy as varying smoking directly, which would also work to identify a smoking->cancer effect.
Without experimentation, there is no way to distinguish between the world of smoker’s lesion and the world of carcinogenic cigarettes.