For better or worse, motherhood is a hot-button topic. Given how universally it’s experienced, pretty much any writer of the female persuasion feels compelled and qualified to weigh in on it. So a growing Mother’s Day tradition — along with flowers and brunch — is the annual deluge of books, articles and blog posts by moms justifying their choices, discussing the aphorisms of motherhood, and basically hauling out whatever political ax they have to grind. For example A, see Dr. Laura Schlessinger’s recent tome, In Praise of Stay-at-Home Moms (though there are others on the “other side” of the debate, whatever that happens to be).

Whenever we deal with something as loaded as motherhood, I personally think it’s important to base our opinions on the facts. So here are a few that I find interesting:

First, the vast majority of mothers are in the workforce to some extent. Even the majority of moms married to men earning over $120,000 a year are in the workforce.

On the other hand, even those who are working full time hardly log the sweatshop hours that some traditionalist writers seem to think characterize paid work. According to the American Time Use Survey, the average married mom in a 2-income couple who works full time puts in 36 hours per week. Her husband? About 41-and-a-half.

Another interesting number: there are 168 hours in a week. If you sleep 8 hours a night, that leaves 112 waking hours for other things. In other words, the average mom who works full time still has 76 hours per week to devote to her children, her marriage, her personal life, maintaining her home, etc.

That sounds like a lot, and it is. Obviously, her children aren’t going to be awake for all of those 76 hours. But here’s another interesting number from the American Time Use Survey. Stay-at-home married moms, on average, spend only 18 hours per week on childcare. Of that, about 8 hours is spent on their physical care. Less than 4 hours is spent actually playing with children. Stay-at-home moms, on average, spend about 38 minutes, weekly, reading to or with their children, and they spend about 1.75 hours on education related activities.

When I point these numbers out to people, they’re amazed they’re so low. There are a variety of reasons for this. For starters, the average stay-at-home mom does not have babies. Children spend very few years in that infant state when they are at home all the time. If a stay-at-home mom’s children are, say, 6 and 8, they are out of the home, in school, for about 35 hours a week. Perhaps not coincidentally, this is almost the exact number of hours the average mom with a full-time job works.  Given the rise of preschool for 2-5 year olds, children are often out of the home for many hours weekly even before school starts. They simply aren’t available to be invested in for all the hours that they might be.

And even when it comes to moms of younger kids, there is this reality of human nature. Most office workers do not spend 100% of their time devoted to the substance of their work. This is why Facebook is as popular as it is — plus emails, phone calls, lunch hours, water cooler gossip, etc. Why would anyone think that the average stay-at-home mom would devote 100% of her time to her main job of nurturing children either?

Obviously, some women do better than others. I would venture to say that, oh, about 50% do better than average. And 50% do worse. The point is also not that stay-at-work moms spend an equal amount of time devoted to high-impact activities such as reading with children as their counterparts who are not in the labor force. They don’t. It’s just that there is nothing about opting out of the workforce full time that guarantees that a woman will invest most of that time in her children. Indeed, it is quite possible for a woman to work 36 hours per week and invest an equal amount of time in her kids as a woman who is not in the workforce. Frankly, it’s possible to work 50 hours a week and still come out ahead.

Here’s another interesting statistic: When women take 3 or more years out of the workforce, they lose 37% of their earning power, according to Sylvia Ann Hewlett’s book Off-Ramps and On-Ramps. One can debate whether this is fair — it probably isn’t — but it is currently true. Since the majority of women who take time out of the workforce do plan to return someday, it’s also a big problem. In this economy, men have absorbed the lion’s share of job losses (with the unemployment rate hitting 8.9% in April, according to numbers released this morning). So newspapers are filled with stories of “Economoms” trying to move back into the workforce after time out to make up for sinking household incomes. And they are having a devil of a time, even before dealing with the fact that their earnings will be a lot lower than if they’d never opted out.

So, given that the average mom with a full-time job still has plenty of hours to invest in her family — easily as much as the average stay-at-home mom if she desires — is it worth losing 37% of your earning power? I’d say no, though people hate talking about numbers when it comes to things like motherhood. Did I mention it was a hot button topic?