Is well-being U-shaped over the life cycle?

Blanchflower & Oswald (2008) present evidence that psychological well-being is U-shaped through life. Using data on 500,000 randomly sampled Americans and West Europeans, the paper designs a test that can control for cohort effects. Holding other factors constant happiness reaches its minimum middle age. The U-shape in age is found in separate well-being regression equations in 72 developed and developing nations. The authors also note that American male birth-cohorts seem to have become progressively less content with their lives.