[aapeli]

This is a hidden case of confounding. In particular, you would expect a question such as "in uncertain times I usually expect the best" to be very heavily confounded with your chance of making it through uncertain times (in the past and in the future).

Yes, they controlled for basic things like some generic concept of health, diet and smoking, but there's so many things that are hard to control for.

As a simple example: what if you have some rare genetic disease that's not controlled for but will likely kill you?