And that's not a bad thing.

Experts define being happy as having positive emotions most of the time. Positive emotions are healthy, prolong life, make living pleasant and feel good.

A researcher at the University of California at Los Angeles found a direct link between the nervous system, the immune system and other functions in an emerging field of study called psychoneuroimmunology. Studies have nailed down the effects of laughter, happiness, stress and bad feelings on the immune system and other biological systems.

In short, happy people and people who laugh a lot generate chemical health benefits that help them live longer and have more fun while doing so.

But that's the clincher — how do you generate positive emotions (we've got some tips), and how do you know when you've generated enough?

Feeling in control

Psychologists gauge how happy a person is by comparing positive and negative emotions over a period of time, says Randy J. Larsen, chairman of the Washington University Department of Psychology.

"The happier you are, the fewer bad days you have," Larsen says. "An average person has seven of 10 good days, while a really happy person may have nine of 10 good days on average."

Dr. Miggie Greenberg, assistant professor at St. Louis University School of Medicine's Department of Psychiatry, says the level of control a person feels can be a measure of happiness.

"Rather than happiness, I would like to think about optimism," says Greenberg. "If we were happy all the time, we'd be bored. We purposely seek out scary movies, sad books; we look for experience that isn't necessarily happy.

"But when we look at it as optimism, the key to happiness is feeling a sense of internal control. We can manage our internal world — it's somewhere we can get some respite and internal control."

People who are optimistic have more control and a better handle on life, live longer, persevere more, have more friends and generally are happier, Greenberg says. Paradoxically, pessimistic people tend to have a better grasp of reality — not that that's necessarily healthy.

Greenberg echoed what all of the mental-health professionals said: Before seeking happiness, clear up clinical depression. That's an illness, she says, not a sadness. This means seeing a professional, maybe even taking medication and having short- or long-term mental-health therapy.

Maximizing potential

The focus on happiness has prompted the mental-health community to take a new look at what it is. The findings so far: Happiness is more than simply not feeling bad, says Larsen.

Before the 1980s, mental-health care involved trying to fix what was wrong. But in the '80s a new discipline emerged: "positive psychology," the study of what people do right.

"Now we study what keeps people from maximizing their potential," Larsen says. "What keeps people from being happy, and not just not depressed."

One of the striking findings: Nothing that was thought to cause happiness really does.

Money can't buy it

Wealth is a source of comfort, not happiness, experts agree. "The dominant view in Western society is that happiness is having what you want," says Larsen. "A lot of people in America believe that they'll be happy when they get that first million, that Porsche Targa convertible ... "

Surprise: "All the research shows that doesn't work."

People who suddenly become wealthy tend to sink to their same level of happiness as before the windfall. In addition, wealthy people tend to be no more or less happy than anyone else.

Larsen recalled that a study in Michigan of lottery winners found that people who won got a mood spike, but six months later were no different from people who hadn't won anything.

Researchers also have found that gender, education, religion, race and age make no difference when it comes to happiness. In other words, happiness had little to do with external circumstances.

The one exception is for people living in poverty. Larsen says that people who can't meet their basic needs will have trouble being happy.

Larsen considers the lack of a demographic effect on happiness a good thing.

"Demographic conditions are very difficult to change," he says. "What if you found wealth was related to happiness? The prescription would be to go out and make a million. Not everyone can do that."

Live your values

Joanne Waldman says people who ask her how to be happy tend to be people who lack balance.

Waldman is a life coach who helps people plan retirement, careers and other life endeavors.

Executives often speak to her about spending 80 percent of their waking hours working.

"If they're not spending any time on themselves, can they truly be happy?" she says. "Obviously, this didn't make them happy. Starting work on yourself makes a difference."

In searching for a person's road to happiness, Waldman asks questions such as, " 'What's the happiest time of your day, of your week, of your month, of your year?' Answering that is the first step to getting in touch."

She asks clients to define what they consider being happy. "That means getting in touch with what they value."

Unhappy people are often those who aren't living their values, she said.

This doesn't mean packing up, leaving the family behind and running away to live on a beach, she says. "But maybe if you have kids now and you can't leave a job, you can start planning for when the kids are gone and you have time to work on yourself."

Act happy, be happy

Think like a happy person.

Researchers say not only is it possible to be happy, but it's doable on a conscious level — it's not simply the luck of life's card game.

Larsen and Greenberg say happiness is a proactive endeavor. It not only can be felt, it can be achieved.

Larsen has co-written a textbook, "Personality Psychology," that includes a section on being happy. The condensed version: Act more like an extrovert and less like a neurotic.

Here are some examples of extroverted and neurotic behavior:

Extroverts:

Are sociable. Extroverts enjoy people. They join groups, they talk a lot, they like being with others.

"You can change to extroverted behavior, and that will change your happiness," Larsen says.

Something to try: Don't spend so much time alone. An unhappy person will find he or she is spending a lot of time alone.

Are active. Extroverts are vigorous; they're energetic and they exercise.

"There are psychologists who treat depression with exercise," Larsen says. "There are lots of positive benefits to being in shape and being active — especially (when you're) older. The older people who suffer depression are the ones sitting alone instead of getting out on the golf course."

Things to try: Keep moving, find things to do, put the things you've always wanted to do on your schedule — then do them.

Seek novelty. Do new things, says Larsen. Extroverts "like trying the new flavor of coffee, meeting new people, studying a foreign language, doing different stuff, going to a new neighborhood to make new friends — they like diversity. These are things you can do easily if you put your mind to it. You can say, 'I'm going to do one new thing today that I've never done before.' Or, 'I'm going to spend an hour with a group of people, or I'm going to call someone and talk for a while.' "

Things to try: Order something different from the menu of your favorite restaurant, see that movie that your spouse has been trying to get you to see, visit a place you wouldn't ordinarily visit. Discover, discover, discover.

Wear rose-colored glasses. Studies show that people who see themselves as happy can be as happy as they wish, regardless of how others see them, says Larsen.

"The illusion theory that's going around is that being happy also means living in a little bit of an illusion, whether or not your friends see you that way," he says. "Thinking of yourself slightly better than you deserve is probably healthy."

Something to try: Adopt a good outlook, which may get you through bad times.

Neurotics:

Are pessimistic. They choose to look at the problems and not the benefits. "They have trouble finding the good in situations — the glass is half-empty," Larsen says. "It leads to the expectation of bad things."

Greenberg says pessimists tend to see problems as long-term inadequacies that spell doom rather than short-term mistakes that will end soon. "A bad grade is one bad grade, not the end of the world," she said.

Solution: Keep things in perspective. "This, too, shall pass."

Are complainers. There's always something wrong, and nothing is ever good enough.

"What that does is drive people away. No one wants to be around them because they're such a downer," says Larsen. "You can monitor yourself; when you sit down to talk, don't complain."

Solution: Think before you speak. If you're about to badmouth someone or something, don't. If you're going to complain about your life, don't. Look for the good and discuss that, or listen to someone who is discussing good times.

Blow things out of proportion. "Neurotics aren't good at keeping things in perspective," Larsen says. "Project yourself beyond the problem. First try to change it, but when you can't, you have to change how you feel about the problem or what you think about it.

"Neurotics lose sight of the good things going on in their lives and dwell on the negative things. Decide not to do that."