Americans often get stereotyped as sunny, optimistic people. According to Pew data, that stereotype has some basis in fact: by developed world standards, Americans have an unusually positive outlook — very unusual.
This chart, courtesy of Pew's George Gao, draws on data from Pew's Global Attitudes Survey. For each country, it shows the percentage of people who were likely to describe today as a "particularly good day" as well as that country's average income level.
They found that people in the developing world were generally more likely than their developed world peers to give the more positive assessment of their day. But Americans were a major outlier:
The weird thing about this result is that, while the "is today a good day" metric is certainly interesting, it doesn't track very well with average happiness. Generally speaking, richer countries are happier countries. So something else has to be explaining the positivity gap — and America's odd outlier status.
The US is an outlier from other developed countries in a number of ways. One other, for example, is religiosity. Gao's data also shows that richer countries tend to be less religious than poorer ones — except for the US. Just under 60 percent of Americans say religion "plays a very important role in their lives;" that figure is closer to 30 percent in most developed world nations.
There's evidence that religious people tend to be more optimistic. One study, which looked at 93,000 women, concluded that those who went to services "at least once a week" were substantially (56 percent) more likely to show high levels of optimism on a test assessing people's view of the world. It's possible that this could be one factor in the US's divergence on the chart above.