[dis-sys]

> then that is a very relevant variable to take into account.

but that variable has nothing to do with whether the procedure itself is effective or not.

[bstpierre]

The question in this context is whether it’s an effective public health measure to recommend the procedure to a population: specifically, does it reduce the number of deaths over a given period?

Whether it’s effective on an individual basis is a related, but different, different question.