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America is still the richest country in the world, but it's not one of the happiest. How much is too little? How much is too much?

Editor's Note: This article is part of "The Ten Today," a series that examines the Ten Commandments in modern society. This story explores the tenth commandment, "Thou shalt not covet."

At one point in her life, Linda Tirado was working two jobs, and she didn't have a car.

She woke up at 5 a.m., walked two miles to work, waited tables until noon, and walked back home. After she got cleaned up, she walked three miles to her bartending job where she worked until 1 a.m., and then walked back home. Or, if she was lucky, she bummed a ride.

They say money can't buy happiness, but people who are struggling to get by, like Tirado, experience lower levels of well-being — and research bears that out.

Crunching Gallup poll data, the Brookings Institute found that Americans who reported the lowest levels of well-being also made less than $2,000 a month, which coincides closely with the 2013 federal poverty guideline level for a family of four. According to Gallup, not only are those in higher income brackets less likely to feel depressed, they are also less likely to experience physical pain and “negative experiences” like anxiety and worry.

Other research over the past few years has given us a clearer picture of the relationship between what we have and how we feel. It turns out that perhaps money can buy happiness, but only to a point — $75,000, to be exact. An oft-cited Princeton study from 2010 found that a salary of $75,000 per year was the level at which security and happiness reached a high point, but that increases beyond that weren't correlated with greater happiness.

Experts say wealth can bring its own kind of suffering, and that the difference between feeling contentment and feeling like we are going without also has to do with comparing ourselves to others — or, in the language of the tenth commandment, coveting. Researchers refer to it as "relative deprivation."

"There are hedge fund managers who are not satisfied with $10 million," says Ron Anderson, a former professor at the University of Minnesota who studies compassion, suffering and well-being. "They need a jet and a yacht, and another $50 million to feel satisfied."

Too little and too much

The landmark Princeton study claiming that the exact amount of money Americans need to be happy is $75,000 a year was conducted by economist Angus Deaton and psychologist Daniel Kahneman in 2010. It asked 450,000 people how they had felt the previous day and whether they were living "the best life possible" for them. The poll also asked about their income.

The researchers found it's easier to feel ground down by your problems when you have less income. For example, among divorced respondents, over half of those who made less than $1,000 a month reported feeling sad or stressed the previous day. That dropped to 24 percent among those making $3,000 or more.

At $75,000 a year, that effect disappears. "It seems like a plausible number at which people would think money is not an issue," wrote author Deaton. It appears to be the benchmark at which people can do things that make them feel good.

That seems to correlate with Tirado's experience. Interestingly, Tirado, the author of "Hand to Mouth: Living in Bootstrap America," was lifted out of poverty by writing about the challenges of being poor. She wrote a blog post explaining the trials of poverty that went viral that led to a book deal that allowed her to quit her minimum wage jobs and move into higher-paid writing work. For her, the benchmark for feeling like you have enough is being able to budget and plan ahead, rather than just make it from paycheck to paycheck.

"You want enough to make rent, pay for utilities, and comfortably know that if your water heater breaks, you're not hosed. You want to know that if your car breaks down, insurance will cover it."

However, once we get more than we need, material possessions become a burden and can reduce quality of life, says Ron Anderson.

"If you get an expensive new car, you don’t want to take it places, and you feel anxiety. You buy a huge house, and you're afraid to leave it," says Anderson.

Colleen Preston began to feel the burden of her 4,000-square-foot house in southeastern Connecticut after her two daughters had grown and left the house.

"It was $700 a month just to heat," says Preston. She lived on a quarter-acre, and keeping up the yard and property was a huge undertaking. Three years ago, she sold her 4,000-square-foot home and traded it for a 900-square-foot house in a retirement community in nearby Cape Cod, Massachusetts.

She had to get rid of most of her stuff to make the move, and she doesn't miss it. "It's actually a relief," says Preston. "I feel light."

Preston isn't the only one who has found that things like a sprawling home can be too much of a good thing. In a February Trulia real estate poll, 43 percent of the 2,000 people who responded said that their ideal home is bigger than the one they live in now. But the one group that wanted to downsize? Those living in homes larger than 3,200 square feet. Of that group, 26 percent wanted to downsize.

"As you get saturated with goods and wealth, you lose a sense of meaning and purpose," says Anderson.

Comparison and deprivation

Anderson's studies find that Americans report a similar amount of suffering to those in other nations, which raises the possibility that affluence might produce its own kind of suffering, he says.

This goes back to the idea of "relative deprivation," or comparing our own situation to those around us. The effects are quite real.

A recent study from the Urban Institute found that poor Baltimore teens feel the effects of poverty more keenly than their counterparts in poorer countries, reporting lower well-being than teens in New Delhi and Nigeria.

Part of this is due to violence and social problems in urban Baltimore neighborhoods, but part of it is because of expectations and perceptions, says Zaneta Thayer, who studies suffering and discrimination at the University of Colorado.

"There is stress associated with not having what you want," says Thayer, and that can be real and valid, especially if you suffer material need or don't have the same opportunities as other people around you.

"If you're in Baltimore, you're surrounded by billboards and TV and neighborhoods where people have access to things that you don't," she says.

But feelings of going without also extend to those who don't have real material deprivation. There's material suffering, and then there's emotional suffering, and the well-to-do seem to have their own existential crises. If you're a millionaire among multimillionaires, it doesn't feel like enough.

"If you're a millionaire among multimillionaires, you're struggling to keep up with the cars, the private school tuition, the place in the Hamptons, and feeling stressed," says Anderson.

There is evidence in Gallup data that stress levels in American have been going up slowly over the last 10 years, he says. "It could be related to terrorism and safety. But I think it’s related to dissatisfaction with not having everything, especially in the wake of the recession."

Giving and purpose

Perhaps the best evidence that money doesn't buy happiness is that the happiest countries in the world aren't in North America or Europe — they are in Africa and South America.

What do these countries have in common? Gallup data shows they have the highest scores in terms of purposefulness — they have tight communities with strong ties to church and family.

"As we acquire more, we have more decisions to make and we make them to satisfy ourselves rather than a group or community," says Anderson.

Poor Americans also give a larger percentage of their money to charity than rich people do, and giving creates a positive feedback loop. "Giving to other people makes you feel happier, more connected," says Anderson.

Connectedness and closer ties to community have been among the benefits of Preston's downsizing. Before, she lived on an isolated quarter-acre lot. Since moving to a small retirement community, she knows all of her neighbors. She's on the homeowners' board, and everyone knows her name.

"Community is a big draw for me here," she says. "It's become more important to me."

Once a person's material needs are met, things like relatedness, purpose and mastery of skills become higher indicators of happiness. Much of what Americans experience are "First World problems," says Anderson, but they impact us nonetheless.

He points to the website mymiserablelife.com, where down-and-outers post everything from breakups to bad luck.

"Halfway around the world someone might be delighted to have the things they have — their job, their lifestyle," he says. "If they lived somewhere else, they would have different problems."

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