I have first asked this question on physics.SE (where I personally believe it belongs), however it was suggested that this question better fits here, so here I am.
My understanding of probabilities in many worlds is following:
If I would decide to start smoking and we know that 10% of smokers get cancer that means that in 10% of all worlds during my lifetime I would get cancer (assuming I would smoke average and I am genetically average to get cancer and average in every way).
or another example:
If I would decide to start building parachute jumping and we know that 5% of building parachute jumpers die in the process that means that in 5% of all worlds where I made such decision I would die from jumping (assuming I am average jumper and average in every way)
Do many world probabilities can be understood in such a way or they are something completely different? If not how should I understand them?
If a smoker getting cancer depends deterministically on possessing some particular characteristic which is present in 10% of the population you will (or will not) have this characteristic in all worlds that split from the present, so you will get cancer (or not get cancer) in every world that is derived from the present one.
But if a smoker getting cancer depends on some random particle decay (or whatever), then in 10% of all worlds you will get cancer and in 90% not. (lots of caveats are needed with this model, such as the "event" has not already occurred converting this model into the former, or ...)