"Those who work longer hours in Europe are less happy than those who work shorter hours, but in the U.S. it's the other way around," said study author Adam Okulicz-Kozaryn, a clinical assistant professor of public policy at The University of Texas at Dallas. "The working hours' category does not have a very big impact on the probability of happiness of Americans."
The study, based on survey data, can't tease out whether work causes happiness or unhappiness, though the researchers speculate the effect has to do with expectations and how a person measures success.
Okulicz-Kozaryn used surveys of European and American attitudes for the study. The surveys included questions about the number of hours worked and asked respondents to identify if they were "very happy," "pretty happy" or "not too happy."
They found that the likelihood of Europeans' describing themselves as "very happy" dropped from around 28 percent to 23 percent as work hours climbed from under 17 hours a week to more than 60 hours per week. Americans, on the other hand, held steady, with about a 43 percent chance of describing themselves as happy regardless of working hours.
The results held even after the researchers accounted for possible confounding factors, such as age, marital status and household income.
Because of a lack of research in the area, Okulicz-Kozaryn said it's not clear longer hours are the cause of happiness or unhappiness here. "It's quite difficult to argue causality," he said.
Without hard data, there are a number of potential explanations for why happiness may differ when it comes to work hours. [5 Things That Will Make You Happier]
"It depends on what one's feeling is about the aspirations of Europeans and Americans," said Richard Easterlin, a professor of economics at the University of Southern California, who was not involved in the study. "We don't have a lot of good evidence on that."
He added, "I feel Europeans are more inclined to enjoy life and enjoy leisure, and Americans are more likely to be pursuing income and increasing their income. There's a difference in the structure of aspirations." However, "I'm not sure I could give you concrete evidence to that effect."
Americans may be onto something: Past research has shown wealth can bring happiness, particularly if a person's income is greater than their peers. Another study suggested that as income increases, so does a person’s overall satisfaction with life. However, that money lift didn't mean more moment-to-moment enjoyment of those days, which instead depended more on social and physical factors, such as whether a person smoked or spent the day alone.
Easterlin and Okulicz-Kozaryn agreed that perceptions may also play a big role, as people who believe their hard work has a greater impact on their success or upward mobility may be happier working more.
"In some countries in Europe, the income mobility may be higher, for instance in Germany," said Easterlin. "It's not really that hard work brings more success in the U.S. than in Europe, it's what people believe in."
Okulicz-Kozaryn said happiness working longer hours may be a product of the American dream — not of its reality, but belief in the dream itself.
"The idea that hard work brings success and the whole idea of the American dream ... is really artificial and made up by public policymakers and politicians to attract immigrants," he said, explaining that studies on the topic indicate that Europeans have similar levels of social mobility and a similar correlation between hard work and success.
Okulicz-Kozaryn noted that further research could be done on areas such as tax rates to better understand the impact of longer working hours. The theory is that Americans, paying lower taxes than their European counterparts, may be happier to work longer hours, as there is more cash going into their pockets.
Easterlin said further research should compare Americans with people in a specific European country rather than the continent as a whole, as it would allow a better understanding of the values of each place.
"Happiness depends upon satisfaction with your income, satisfaction with you family life, satisfaction with your work, satisfaction with your health," he said.
"People trade off work and leisure," Easterlin explained, and so any attempt to explain the results of this study would have to take that into account. "[Happiness] has to do with what you think the goals are of people in the two countries."
The paper appears in the April issue of the Journal of Happiness Studies.