It's difficult to study something that nobody can define in a non-circular way. From McCloskey: Happyism - The creepy new economics of pleasure. She makes the point that much of this is pseudo-scientific.
A quote from her very interesting essay:
...in the eighteenth century, our earthly happiness became important to us, in high intellectual fashion. By 1776, “life, liberty, and the pursuit of happiness” was an unoriginal formulation of what we all, of course, now admitted that we chiefly wanted. John Locke had taught, in 1677, that “the business of men [is] to be happy in this world by the enjoyment of the things of nature subservient to life, health, ease, and pleasure”—though he added piously, “and by the comfortable [that is, comforting] hopes of another life when this is ended.” By 1738, the Comte de Mirabeau wrote to a friend, recommending simply, “[W]hat should be our only goal: happiness.”
“Our only goal.” To see how strange such a remark is, consider whether it could have been uttered by a leader of opinion in 1538. Martin Luther? Michelangelo? Charles V? No. They sought heavenly, artistic, or political glory—not something so domestic as happiness. Yet, in the late seventeenth century, even Anglican priests commenced preaching that God wanted us to be happy as much as holy. They called it “eudaemonism.” Anglicans and, astonishingly, some New England Congregationalists turned against the old, harsh, Augustinian-Calvinist line. We are not, declared the eudaemonists, mere sinners in the hands of an angry God, worms unworthy of grace. We are God’s beloved creatures, his pets.
The eudaemonistic turn was a Very Good Thing, resulting in fresh projects to better our stay here on Earth, some of them remarkably successful. Democracy was one, since, if you followed the fashion for universal happiness, it became impossible to go on insisting that what really mattered was the pleasure of the Duke or the Lord Bishop. Enlightened despots of the era claimed to seek the good of all, which paradoxically gave the populace the idea that maybe they themselves could do it.
I will remind our readers that Freud (yes, still relevant in many ways but not in all ways) had a somewhat tragic view of life and figured that pleasure and joy certainly matter, but that, overall, ordinary - "non-neurotic" - unhappiness is man's fate. Some days, I agree with that, other days, I don't.
By coincidence, Schneiderman's Unhappy or Depressed? I will need to return to the Dalrymple piece he quotes, later.