Yeah, without more information about the specific people involved, it's difficult to respond with a definite answer. Your logic certainly makes sense.

The group size thing is interesting. Your argument that an individual would be more likely to volunteer in a large group (as there are more lives to save) makes sense. But it's also possible that a larger group could reduce any one individual's feeling of personal responsibility, and therefore it might reduce the chance of someone volunteering.

I agree that someone should be more likely to volunteer in the car example. They're not changing their own chances of winning, and given that they didn't have a car before, they're not exactly 'losing' anything. I've been surprised by the number of people who've argued that people would be less likely to volunteer in that situation.

Anyway, it's all very interesting! :)