I noted exactly that in my comment. Yes, not all the population can go on a cruise. No, it's not like it's only the healthiest 20% of the population that can. If I randomly sampled the population I'd expect the majority to be capable of a cruise. What do you think cruises are like?
If you agree that they are not a random sample of the population - they are healthy enough to be fit for travel (like the majority of the population) you are not trying to contradict ant6n's comment as I thought. I misunderstood, my apologies.
and it's not a small travel (e.g. the British tourists that went on board the Diamond Princess).
If you are not in good health at the beginning, you don't adventure yourself 10 hours+ from your home.
So this group is likely in better shape than average population.
