Latest studies say American men's average happiness level has been going up while womens' have stayed the same, largely due to both increasing social demands from women as well as increasing economic ambitions by them.

A big reason that women reported being happier three decades ago — despite far more discrimination — is probably that they had narrower ambitions, Ms. Stevenson says. Many compared themselves only to other women, rather than to men as well. This doesn’t mean they were better off back then.