Within the U.S., a commonly cited data source is the General Social Survey (GSS). This has been measuring general well-being levels every one or two years going back to 1972, and since then, has always shown that the percentage of people who say they are “very happy” hovers between roughly 30 and 35 percent, while the percentage of those who are “not too happy” sits around 10 to 15 percent. – The Atlantic