Inside/outside cats live nearly as long as inside only cats plus they have a much more interesting & varied existence.

The studies you have quoted returning average life span of less than 10 years, includes feral cats, strays & very young kittens.

If a study looked at inside/outside cats who were older than 6 months, neutered and trained to be outside, the average life expectance leaps to 15 years to 18 years, the drop from the slightly higher life range for inside cats, takes into account the 2% lifetime chance a cat has of dying on the roads.

In reality if the cat is well cared for there is very little difference between an inside/outside cat and an inside only cat.

I think I will do a study on the issue when I start by cat behaviourist course in October.