London: Convention tells us the route to happiness is having children. Yet, a researcher has claimed that marriage without kids is actually the key to bliss.

Prof Daniel Gilbert of Harvard University has said that married life is the key to happiness but having kids can ruin it all, and couples only recover their blissful existence once their offspring have left the nest.

According to him, a desire by couples to get a return on the time and money they have invested in their children is part of the reason they persuade themselves that their offspring are enhancing their lives.

"Figures show that married people are in almost every way happier than unmarried people -- whether they are single, divorced, cohabiting. Married people live longer, married people earn more money per capita, married people have more sex and enjoy it more," Prof Gilbert said.

However, when couples have kids, happiness plummet. "Children do seem to increase happiness (while) you are expecting them, but as soon as you have them, trouble sets in. People are extremely happy before they have children and then their happiness goes down, and it takes another big hit when kids reach adolescence."

"When does it come back to its original baseline? Oh, about the time the children grow up and go away. Money was part of the reason that couples believe their children brought them happiness," The Daily Telegraph quoted him as telling the Happiness and its Causes conference.

Psychological studies have shown that people appreciate products more if they pay more for them. "We pay for (children) in time, attention, blood, sweat and tears -- what kind of idiots would we be to devote all of that to the rearing of our young if they didn t bring us some happiness?" he said.