Statistics question

[TravelGal]

At least I think it's statistics. Law of probability? Odds? I've been thinking it's the number of square feet per passenger that matters on a cruise ship--all other safety precautions being equal--not the number of passengers. Social distancing and all that.

A client says having, for example, 2000 passengers rather than 100 passengers on a ship raises the changes of catching something no matter how large the ship is or how many square feet per passenger that works out to be. Given that "small ships" will be allowed into Canada this summer, it looks like that must be correct. Cabin size and size of common areas comes into play for exact square footage comparisons but, overall, what say ye? Theoretically speaking.

[WickerBill]

I'm perhaps the very worst person to answer this, but it seems to me both are true.

Yes, having 2000 instead of 100 raises the odds.

Yes, having 2000 in 500,000 sq ft lowers the odds vs 2000 in 200,000 sq ft.


My perception is that the intersection of those two points is important. When people per square foot raises the odds over a certain threshold, it's too much. For example, going from 3 people to 5 people in Madison Square Garden raises the odds of transmission almost imperceptibly. But going from 3,000 to 5,000 might make it too risky.

All about that threshold, I would guess.

[pfc_m_drake]

From a pure 'statistical modeling' standpoint, you have roughly the same chance of contracting COVID in both cases. That's because the occurrences of COVID in the community are roughly constant. For example, let's say the rate of COVID is 6 people out of every 100. That means (statistically) there are 6 positive cases on the ship that caries 100, while there are 120 positive cases on the ship that carries 2000 people.

That's 'simple' modeling, in reality there's much more to consider. In some sense, a better metric could be number of passengers (and crew) per square foot of ship space. In that sense, you might imagine that it would actually be easier to contract COVID on a Viking River Cruise Ship with 100 people (e.g. a small ship filled to 50% of its nominal capacity) than it would be on the Symphony Of The Seas with 2000 people (e.g. a mega ship filled to 29.5% of its nominal capacity). The theory is that your interactions wit infected people are actually much greater on the smaller Viking Ship than they would be on the larger Royal Caribbean Ship.

Unfortunately it gets very complicated very quickly, but for the purpose of this discussion - specifically addressing your client's concerns - I don't think the answer is as clear as he (or she) may believe.

[TravelGal]

Excellent food for thought, both of you. The interaction level is why I thought it wouldn't matter if there were 2000 or 100 as long as the number of square feet were constant. It can also be expressed as percentage of capacity. I thought the same level of risk exists whether you are on a large ship or a tiny one as long as they were both, for example, 25% full. Then complexities come into play when you figure the large ones have salons and play areas and gyms adding to the square footage while the small ones might not. Meaning the more frequently used common areas would be more densely populated on the larger ships.

Good research, pfc, on the ships! :thumbup: It looks like a mandate, when made, will be a maximum of X percent of capacity for all ships. The general public can latch onto this more easily than nuanced rules.

The variable then becomes financial. Will Viking or Royal Caribbean passengers be more eager to sail and fill up the ship to maximum allowable capacity. If not, will the ship sail at all? Whether the Symphony of the Seas can afford to sail at say 25 or even 50% capacity is a topic under discussion right now in travel agent circles.

[pfc_m_drake]

Well, I'm certainly ready to go when the ships actually start sailing, so count me in!

The number I had heard bandied about to make a cruise profitable was 25% capacity. BUT, I have no firsthand knowledge of whether that's true or not. My hope is that the caseload continues on its current trajectory, that the vaccine rollout speeds up, and we can all get back to normal sooner rather than later :thumbup:

That's about as best I can do for optimism these days...