Education, and I regret to say this as an educator, but there's no indication that education has a direct effect on happiness.
Derek BokThe most obvious purpose of college education is to help students acquire information and knowledge by acquainting them with facts, theories, generalizations, principles, and the like. This purpose scarcely requires justification.
Derek BokDoctoral training is devoted almost entirely to learning to do research, even though most Ph.Ds who enter academic life spend far more time teaching than they do conducting experiments or writing books.
Derek Bok