No kids, one kid, four kids: There's no end to the debate over why people decide on a certain number.

But is one family configuration more scrutinized than another? Lauren Sandler thinks so.

She delves into the myths and misconceptions about singletons in a new book, "One and Only." And she feels strongly about the subject, as a journalist and an only child raising an only child with her photographer husband, who's one of two.

The choice of one, the Brooklyn mom said, often is demonized and the pull to have more is strong at times. Based on scores of interviews with academics and only children, the book wasn't intended as a memoir, though Sandler's family is woven throughout.

While she's content and confident that her 5-year-old daughter is doing great, Sandler hasn't escaped the conflict. Her response when her husband suggests he get a vasectomy drives home the turmoil.

"I burst into tears, run up to our bedroom, and throw myself onto the pillows like a heartsick teenager," she writes.

"Despite all the rational information that supports my reluctance to have another kid, all the research demonstrating that only children are fine, all the data suggesting the additional sacrifices another kid would require, making the choice not to have another child is still fraught with conflict. It's an emotional struggle that, it turns out, no set of numbers and analysis can erase."

A conversation with Lauren Sandler:

AP: How has research on raising only children changed in recent years?

Sandler: I don't think it's really changed. What keeps happening is people keep retesting, saying, "Oh, how could it possibly be true that all of these studies from all of these years ago have said that only children are just fine." And so they retest and then they find out, "Oh yeah, only children are fine."

AP: So where does the notion come from that only children are lonely, selfish and maladjusted?

Sandler: I've been puzzling over this for three years, and the best I can come up with is this sort of three-pronged answer.

No. 1, it was a story that needed to develop in an evolutionary biology sense, that in order to thrive as a species we had to have more of us, so that was important. And then we were an agrarian society, and in an agrarian society children were a workforce and a life insurance policy, and if you wanted your family to thrive you needed to have a bigger one.

But then the Industrial Revolution came around, then the women's movement came around. We didn't really come to terms with what women's freedom looks like, and we didn't really come to terms with how much society had changed, and so we kept telling this story. I've talked to researchers who think that it's a story that people need to tell because having more kids is hard and you need to feel like there's a reason behind it.

AP: What drives that nagging pull to have more?

Sandler: I think that as parents we want our kids to be happy and to thrive. We want our families to be happy, and we have society telling us if you have one kid, your kid's going to be really unhappy. You're going to have a miserable misfit of a child, but if you give your child a sibling you will have a happy family.

The data tells us that most people have their first child for themselves and the second child for the benefit of their first. I feel like if you want two kids, three kids, five kids, no kids, great. Do what your heart tells you but don't do what society is whispering in your ear, especially when it's based on such fallacy.