"Correlation does not imply causation" - repeat three times before looking at the results of any study of data. Via the LEF News, reports of a correlation between air quality and life expectancy in the US: "The findings were based on research in metropolitan areas in six states ... participants, ages 25 to 74 when the study began, were followed for a period of 24 years. Air quality improvements were matched by a proportional drop in death rates from cardiovascular disease, respiratory illness and lung cancer, the study found." I would be willing to wager that the correlation has more to do with the relative wealth of these areas and those who make the economic choice to live there, as well as access to medical technology and lifestyle choices. Things are rarely as simple as a two-parameter study casts them to be.

Link: http://www.lef.org/news/LefDailyNews.htm?NewsID=3946