"Overall quality of life" can mean a lot of different things, depending on how you measure. Do you mean the arithmetic mean, the median, the quality of life of all members of the population, or something else? And while we're at it, it's worth considering how the population is defined -- all Americans? All westerners? All humans?

I've found that the appropriate answers tend to differ considerably depending on these definitions, and there is nowhere near a consensus for which is the right one to strive for.