I happened to stumble across a report from the Pew Research Center on the demographics of happiness. The report was interesting, but very little was actually surprising.
The report finds that income corelates to happiness, as having one's basic needs met can remove some of the most common causes of misery. However, the survey puts all making above $150,000 a year into one bucket, thereby not providing any insight into whether there is incremental probability of happiness upon making $300,000, $500,000, or $1 Million a year. I believe that it is quite possible that there is virtually no marginal increase in happiness beyond an income of, say, $200,000 a year or so, because nearly all material needs are met at this threshold. Additional income can bring only more power, prestige, and fame, but material consumption and the resultant gratification saturates as this point. In other words, if someone making over $200,000 a year is still not happy, it is probably for some reason other than money.
The next question that arises is that of relative vs. absolute wealth. If a person earns more than 95% of the members of his society, he is rich in whatever era he lives in, but even a person of average income today has many technological luxuries that were unavailable to the wealthiest person 50 years ago. This, combined with the rapidly growing ranks of the wealthy as a share of the total population and the tendency of prosperity to move people up the ranks of Maslow's Hierarchy of Needs, could lead to a very slow but steady migration of happiness away from increasingly accessible material consumption and towards more self-actualized forms of human fulfillment.
Beyond wealth, one's worldview has an influence on happiness. When happiness is categorized by political leanings, Republicans have had a stark advantage over Democrats for the last 35 years. This is even during the Clinton years, when Democrats had the most reasons to be cheerful than at any other time, and President Clinton himself had a contagious optimism that contributed towards high consumer confidence and a strong economy. The most obvious explanation for why 'liberals' are perpetually unhappy is that the realities of the real world continue to deliver outcomes contrary to what theoretical 'liberal' beliefs lead them to expect.
Additionally, one particular strain of 'liberalism' departed from the genuinely liberal goal of improving society, and mutated into a religion of hatred towards those who are happier than they are. 'Tax the Rich' might really be intended to mean 'Tax the Happy, because we are jealous of them'. There was a time when the 'left' and 'right' merely disagreed on which approach was more suitable to cause improvements in society, as opposed to today when many on the 'left' have no interest in improving society at all, but merely feign altruism while engaging in a hateful campaign to obstruct or distort the pillars of traditional society from which most non-leftists derive happiness (such as marriage, faith, children, or entrepreneurship). This causes great conflict between their leftist religion and the natural urge of human decency still faintly present within them, and thus leaves them twisted and tortured in self-contradicting misery. The same is probably true of suicide bombers, for that matter.
Since happiness is a natural condition, present when natural needs are met, what does it tell us about which belief systems, activities, and behaviours are more 'naturally' suitable for human life?