翻译原文：

ROME (Reuters Life!) - Americans are less happy today than they were 30 years ago thanks to longer working hours and a deterioration in the quality of their relationships with friends and neighbors, according to an Italian study.

Researchers presenting their work at a conference on "policies for happiness" at Italy's Siena University honed in on two major forces that boost happiness-- higher income and better social relationships -- and put a dollar value on them.

Based on that, they concluded a person with no friends or social relations with neighbors would have to earn $320,000 more each year than someone who did to enjoy the same level of happiness.

And while the average American paycheck had risen over the past 30 years, its happiness-boosting benefits were more than offset by a drop in the quality of relationships over the period.

"The main cause is a decline in the so-called social capital -- increased loneliness, increased perception of others as untrust worthy and unfair," said Stefano Bartolini, one of the authors of the study.

 "Social contacts have worsened, people have less and less relationships among neighbors, relatives and friends."