原文：How to be happy: What is happiness anyway?

Psychologist Daniel Gilbert knows exactly how happy 5000 people around the world are right now. What has he learned about our ups and downs?

What's so tough about studying happiness?
One problem is that researchers often measure different things and then talk about them as though they were interchangeable measures of the same thing. We can measure how happy someone is in the moment or how satisfied they are with their lives, and while both are interesting, they are not the same. For instance, we now know that once you earn about $75,000 per year, your happiness won't increase with more income but your satisfaction will. So the public policies that will lead citizens to say "I'm satisfied" are not necessarily the same as those that will lead them to say "I'm happy," and so when we make policy we must first decide which of these we want to maximise.

Can we trust what people say about happiness?
There is a widespread belief that it is "objective" to measure muscle contractions and cerebral blood flow but "subjective" to measure happiness by asking people how they feel. That's rubbish. People's reports of their emotions are incredibly reliable and they wouldn't correlate with all the other indicators of emotion if they weren't. The issue isn't what you ask, but when. Asking people to report how they felt yesterday when watching TV is not particularly useful because retrospective reports are notoriously biased. Ideally, you want to ask this question when people are in the middle of watching TV. Unfortunately, until recently, collecting data this way has been wildly impractical.

How have you tackled this timing issue?
Trackyourhappiness.org is a research project that uses smartphones to solve the problem. We send volunteers text messages asking them to report how they are feeling and what they are doing at that very minute.

Over 5000 people from 83 countries have signed up. Are there any surprises in the data?
Yes. For example, most of us think that it is fun to let our minds wander (which happens about half the time). But our data show that when the mind is wandering, people are less happy, not more. People are happiest when thinking about what they are doing and not something else. This is true even when commuting or washing up.

Why? Surely happy thoughts make us happier.
I always thought so, and so did everyone I know, but we were wrong. People who are "here and now" seem happier than those who aren't. That's one reason social interaction makes people happy. When you talk to someone, your mind rarely wanders because you are listening and thinking about what to say. Interaction keeps us tethered to the moment. It doesn't allow us to float away.

What else makes us happy?
There aren't many surprises. As your grandma might have said, the list includes friendships, health, money, sleep and sex. To my mind, the only real surprise is children, who have a small but reliably negative impact on happiness.

Is it useful to measure national happiness?
I don't think it is important to come up with a single number - the equivalent of a gross national product index. What we really want to know is whether and why Liverpudlians are happier than Mancunians, whether and why people in this job are happier than in that one. Public policy has always sought to maximise the well-being of citizens, and the reason so much policy is meant to promote economic growth is because we believe it enhances well-being. Now we can measure well-being directly and put such assumptions to the test.

Will austerity bring new ways to be happy?
When people have less wealth than they had, they feel miserable. So people who were doing fine are going to experience pain. But the greatest pain will be felt by those who aren't doing fine - namely, the middle class and the poor. People have basic needs, and when those needs aren't met they feel unhappy. New ways of seeing things won't fill their stomachs.

Should states push to measure happiness?
Of course. If your salary were suddenly halved you would want to know which of your current expenditures contribute to your well-being and which don't. Similarly, we need to know which areas of state spending give us the biggest bang for our buck.

Does your research make you change your life?
I believe my data and I incorporate the lessons into my life when I can. A few years ago, we found that people are much happier with irreversible than reversible decisions because we rationalise the former but not the latter. Someone mentioned this was the essential difference between living with or marrying your girlfriend. If your wife does something mildly annoying you shrug your shoulders, but when your girlfriend does it you wonder if you should keep shopping. As soon as I saw that result I went home and proposed.