Let's play a game. You have to follow the links:
"People's ability to be an agent, to act on behalf of what matters to them, is fundamental (to happiness)"
This is from the APA site: How happy are we? Danes are an 8.2, but Americans only a 7.4
This (same article, best I can tell) is from the USA today: Researchers: Choices spawn happiness
Let's forget the research for a second. Note the stock photo the USA today chose for the article. Is it me, or does it suggest that if a young guy has his choice among hot, mud-wrestling chicks in bikinis, he'd be happier? I don't think that really was the point of the research.
Anyway, here's a good article on how researchers study happiness.