This makes sense.FYI - the Mercer index is not really a "quality of life" gauge. It does not puport to measure many of the things that most people consider in such surveys - things like culture, food, weather, things to do, history, natural beauty, proximity to other things of interest, neighborhoods, etc. It isn't about any of those things.
The Mercer index is used solely to evaluate how much "hazard pay" you have to pay to an executive to relocate somewhere. Pretty much the only thing it cares about is infrastructure, crime, ease of getting in and out on airplanes, and traffic. On that scale, Zurich is the perfect city. Safe, white, clean, new and dull as dishwater.
If you want to see an index of quality of life in the sense that most of us understand it, the best source is probably the Conde Nast or Travel and Leisure magazine surveys. On those surveys of tens of thousands of travellers the favorite city usually is Sydney, Australia, followed by San Francisco.
Of course, if you take into account cost of living, the lists will change dramatically again. San Francisco would drop because it is so expensive. But the Mercer iindex doesn't care about that either - cost of living is meaningless to a high powered international business executive.
Basically, the Mercer index is useless.