I think that should be taken more statistically (though I have no idea what it is) but think if a drug increases life expectancy of 1 in 10 people by 10 years (say by curing/delaying a disease that 1 in 10 people get) then it increases everybody's life expectancy by one year, statistically (Or in this case, Aboriginal life expectancy).

Also one more year isn't much... penicillin/antibiotics would increase life expectancy much more than that (I assume)