[akvadrako]

That suggests something strange though – that those who were invited but non-tested were more likely to die of colon cancer than non-invitie non-testers.

[zerocrates]

I suppose that by refusing to get a colonoscopy even when specifically prompted to do so, you're maybe sorting yourself into a more "unhealthy" group than the general population of non-colonoscopy-havers.

[robertlagrant]

That would make the outcome less surprising.

[bluGill]

It would be unethical to refuse to invite someone with a family history of colon cancer. Thus I think it is perfectly reasonable to assume there is something different.