A new statistical analysis of 10,000 households, whose members were asked questions about their happiness over a 15 year period, reveals that for married parents, each child makes them progressively happier. In contrast, those who are single, separated or living together are more likely to have negative feelings about parenthood.

Writing in the Journal of Happiness Studies, Dr. Luis Angeles, an economist at Glasgow University, said "raising kids makes married people happier" and that "the more they have, the happier they are."

Dr. Angeles looked at the happiness levels of married people before and after becoming parents. He then did the same for those who were not married. He speculates that the reason for the difference in happiness levels may lay in whether children were planned or not:

"People who have decided to get married probably have in mind that they want to have children. But in the case of unmarried parents, children might not be expected," he said.