From the perspective of the species, it's perfectly unmysterious why people have children. From the perspective of the individual, however, it's more of a mystery than one might think. Most people assume that having children will make them happier. Yet a wide variety of academic research shows that parents are not happier than their childless peers, and in many cases are less so. This finding is surprisingly consistent, showing up across a range of disciplines. Perhaps the most oft-cited datum comes from a 2004 study by Daniel Kahneman, a Nobel Prize-winning behavioral economist, who surveyed 909 working Texas women and found that child care ranked sixteenth in pleasurability out of nineteen activities. (Among the endeavors they preferred: preparing food, watching TV, exercising, talking on the phone, napping, shopping, housework.) This result also shows up regularly in relationship research, with children invariably reducing marital satisfaction. The economist Andrew Oswald, who's compared tens of thousands of Britons with children to those without, is at least inclined to view his data in a more positive light: "The broad message is not that children make you less happy; it's just that children don't make you more happy." That is, he tells me, unless you have more than one. "Then the studies show a more negative impact." As a rule, most studies show that mothers are less happy than fathers, that single parents are less happy still, that babies and toddlers are the hardest, and that each successive child produces diminishing returns. But some of the studies are grimmer than others. Robin Simon, a sociologist at Wake Forest University, says parents are more depressed than nonparents no matter what their circumstances--whether they're single or married, whether they have one child or four.

The idea that parents are less happy than nonparents has become so commonplace in academia that it was big news last year when the Journal of Happiness Studies published a Scottish paper declaring the opposite was true. "Contrary to much of the literature," said the introduction, "our results are consistent with an effect of children on life satisfaction that is positive, large and increasing in the number of children." Alas, the euphoria was short-lived. A few months later, the poor author discovered a coding error in his data, and the publication ran an erratum. "After correcting the problem,"it read,"the main results of the paper no longer hold. The effect of children on the life satisfaction of married individuals is small, often negative, and never statistically significant."

-- Jennifer Senior writing in New York Magazine. Lots more here.