We all want to be happy but the problem has always been that you can't measure happiness.
Happiness has always been seen as too vague a concept, as Lord Layard, Professor of Economics at the LSE and author of "Happiness - lessons from a new science" points out.
"There is a problem with the word happiness.
"When you use the word happy, it often has the sort of context of balloons floating up into the sky or something frivolous."
Now scientists say they can actually measure happiness.
Neuroscientists are measuring pleasure. They suggest that happiness is more than a vague concept or mood; it is real.
Social scientists measure happiness simply by asking people how happy they are.
It is argued that what a person says about their own happiness tends to tally with what friends or even strangers might say about them if asked the same question.
Most people say they are fairly happy.
PDAs can be used to measure happiness levels during the day
The leading American psychologist Professor Ed Diener from the University of Illinois, told The Happiness Formula that the science of happiness is based on one straightforward idea:
"It may sound silly but we ask people 'How happy are you 1-7, 1-10?
"And the interesting thing is that produces real answers that are valid, they're not perfect but they're valid and they predict all sorts of real things in their lives."
One type of measurement even tries to record people's levels of happiness throughout the day wherever they are.
Ecological momentary assessment uses hand held computers.
The person being quizzed is bleeped and then taken through a questionnaire.
"The measures are not perfect yet I think they are in many ways as good as the measures economists use," said Professor Diener.
It is a remarkable claim. Simply by asking people, we have a measure of happiness that is as good as the economists' measure of poverty or growth.
And if true, governments could be judged by how happy they make us.
An adviser to the Prime Minister, David Halpern, told us that within the next 10 years the government would be measured against how happy it made everybody.
Power of happiness
Happiness seems to have almost magical properties.
We have not got proof, but the science suggests it leads to long life, health, resilience and good performance.
Standard of living has increased dramatically and happiness has increased not at all
Professor Daniel Kahneman, University of Princeton
Scientists work by comparing people's reported happiness and a host of other factors such as age, sex, marital status, religion, health, income, unemployment and so on.
In survey after survey involving huge groups of people, significant correlations between happiness and some other factors are repeated.
At the moment scientists cannot prove causation, whether for example people are healthy because they are happy, or whether people are happy because they are healthy.
However, psychologists have been able to identify some very strong links.
According to Professor Diener the evidence suggests that happy people live longer than depressed people.
"In one study, the difference was nine years between the happiest group and the unhappiest group, so that's a huge effect.
"Cigarette smoking can knock a few years off your life, three years, if you really smoke a lot, six years.
"So nine years for happiness is a huge effect."
Richer but no happier
Happiness researchers have been monitoring people's life satisfaction for decades.
Happy people have close friends
Yet despite all the massive increase in our wealth in the last 50 years our levels of happiness have not increased.
"Standard of living has increased dramatically and happiness has increased not at all, and in some cases has diminished slightly," said Professor Daniel Kahneman of the University of Princeton.
"There is a lot of evidence that being richer... isn't making us happier"
The research suggests that richer countries do tend to be happier than poor ones, but once you have a home, food and clothes, then extra money does not seem to make people much happier.
It seems that that level is after average incomes in a country top about £10,000 a year.
Scientists think they know the reason why we do not feel happier despite all the extra money and material things we can buy.
First, it is thought we adapt to pleasure. We go for things which give us short bursts of pleasure whether it is a chocolate bar or buying a new car.
But it quickly wears off.
You can't take a grouch and make him giggle all the time
Professor Martin Seligman, University of Pennsylvania
Secondly, it is thought that we tend to see our life as judged against other people.
We compare our lot against others. Richer people do get happier when they compare themselves against poorer people, but poorer people are less happy if they compare up.
The good news is that we can choose how much and who we compare ourselves with and about what, and researchers suggest we adapt less quickly to more meaningful things such as friendship and life goals.
What makes us happy?
According to psychologist Professor Ed Diener there is no one key to happiness but a set of ingredients that are vital.
For added happiness, look for meaning in your life
First, family and friends are crucial - the wider and deeper the relationships with those around you the better.
It is even suggested that friendship can ward off germs. Our brains control many of the mechanisms in our bodies which are responsible for disease.
Just as stress can trigger ill health, it is thought that friendship and happiness can have a protective effect.
According to happiness research, friendship has a much bigger effect on average on happiness than a typical person's income itself.
One economist, Professor Oswald at Warwick University, has a formula to work out how much extra cash we would need to make up for not having friends.
The answer is £50,000.
Marriage also seems to be very important. According to research the effect of marriage adds an average seven years to the life of a man and something like four for a woman.
The second vital ingredient is having meaning in life, a belief in something bigger than yourself - from religion, spirituality or a philosophy of life.
The third element is having goals embedded in your long term values that you're working for, but also that you find enjoyable.
Psychologists argue that we need to find fulfilment through having goals that are interesting to work on and which use our strengths and abilities.
However, there are also many things we experience in life that can produce lasting unhappiness.
Professor Ed Diener identifies two key events which can have lasting effects.
After the loss of a spouse it can take several years to regain the previous level of well-being.
The loss of a job can affect a person for years even they are back to work.
So if you are born grumpy are you always going to be grumpy?
The question of whether we can actually use our knowledge of what makes us happy to lift our levels of happiness permanently is hotly debated by psychologists.
According to the positive psychologist Professor Martin Seligman of the University of Pennsylvania it is possible to lift our biological set range of happiness, at least to some extent if we work at it.
"The best you can do with positive emotion is you can get people to live at the top of their set range.
"So I think you've got about 10 to 15% leverage but you can't take a grouch and make him giggle all the time."