[em500]

Yup.

The study answers a question from health policy makers: Should we invite everyone (in some age group) for a colonoscopy? Based on this study, probably not.

It does not answer questions from individuals: Should I get a colonoscopy? If you have some good reason (symptoms, doctor advice, family history), probably yes (based on other studies, not this one).

[sokoloff]

To the extent that there’s a spread in those answers, a third possibility emerges: how can we, as health policy makers, find a way to make the invitations more effective at converting to administered colonoscopies?

[thaumasiotes]

Why would that be a goal? First you'd need to show that colonoscopies were helpful in general, or that invitations were going to a subpopulation in which colonoscopies were helpful.

[sokoloff]

If colonoscopies are helpful to avoid negative outcomes, but invitations to colonoscopies are not, looking into making invitations better seems like an obvious play to me.

[JamesBarney]

The problem is you can't run a study on colonoscopies that doesn't involve an invitation without forcing people to get a colonoscopy at gun point. Which would both be illegal and never pass an IRB.

[thaumasiotes]

> Which would both be illegal and never pass an IRB.

To be fair, this is not two separate problems. Anyone who's willing to run the illegal study will not care whether they can get IRB approval.

[sokoloff]

You can control for the invitation vs no-invitation and colonoscopy vs no-colonoscopy and analyze the outcomes of all four cells (provided you have enough people in each cell) or the column or row independently.

[thaumasiotes]

You can do that, but you won't learn anything, because the populations within each cell are not comparable to each other.