Having More Kids: Scaling Up

Kid difficulty functionIn the last year of my PhD program I took a course on entrepreneurship in the business school. The professor described entrepreneurs as people who create organizations, in the face of risk and uncertainty, with the goal of producing something valuable.

You could think of parents as people who incorporate themselves into families, despite substantial financial risk and psychological uncertainty, with the goal of producing valuable, successful humans. So, parents are entrepreneurs. Some might even be considered start-up junkies. I’m not sure what to call the octomom, or the Duggars. They’re following the Starbucks model.

As with a supermarket or restaurant chain trying to expand, if the first kid seems to be working out, scaling the family up is a simple, logical next step. Parents develop a prototype child, and, depending on the outcome, they build the business by replicating their initial concept.

So, how bad would another kid be? It depends, of course, on things like your company’s debt-equity ratio and current assets, but, on average, each additional kid should be incrementally less difficult than the last as you learn from previous mistakes and build your diaper-changing and nose-wiping skill sets.

What is your goal for scaling up?

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We recently reached n = 4 and the data seem to support the kid difficulty model. The first is always craziness. Parents aren’t used to the stress of keeping a small, fragile human well and safe. We don’t know which of the standard health guidelines apply at the micro level. As a result, we become hypersensitive to any change which could indicate something serious.

Why is he breathing like that? Was that a burp, or just a baby grunt? So, should I keep burping him? Aren’t you patting him a little hard? You’re supposed to keep your palm open, not in a fist. No, that’s kind of slappy. Seriously, that would hurt my back.

So, he’s been crying for almost 20 minutes – something’s wrong. Is he hungry again? Didn’t you just nurse him? Maybe you should stop eating spicy food, and chocolate. Really? Maybe he’s cold? Turn on the heater. Or hot – check his temperature. 98.7? He might have a fever.

Oh, he probably needs his diaper changed – it’s totally your turn. What?! Is he eating algae? Green? Wait, now yellow!? Again? Where are all these bright pigments coming from? Is that normal?

After the first, you realize that most everything that appears strange and wrong is actually nothing to worry about. He’ll be fine. You’ve made most of the important decisions and the classic mistakes, like letting him sleep naked because he has a diaper rash. You know what to do when he swallows a marble, and, hopefully, you’ve been through the valley of the shadow of potty training. You’ve also learned that kids are pretty resilient to the basic parenting blunders.

Of course, scaling up is only the beginning. It just occurred to me that we’re going to have 4 teenagers, at the same time. I’m afraid.

The Due Date Margin of Error

2008 US gestation distributionWhether you want to schedule a last fling before the baby comes, or this is your nth kid and you need someone to babysit the other n – 1, knowing the margin of error on your due date would make planning a lot easier.

This knowledge can also give dads credibility in certain parenting circles and in baby-related decision making, which may help boost their confidence and moral.

Below are some US margins of error and a few other handy statistics that will quickly prove you are an engaged and caring father. Warning: also included below are some intimidating pregnancy words (e.g., gestation, menstrual, conception). Apologies for any anxiety they may cause.

Information and Sources

It’s hard for a dad to get good information when something like 98.6% of statistics are made up on the spot. Online are a variety of due date confidence intervals, from 12 days, to 18 days, to 4 weeks; so there’s a large margin of error on the margins of error. Also, someone said that 60% of people don’t credit their sources.

Tired of the confusion and in need of a moral boost, as we’re approaching n = 4, I decided to go to a pretty reliable source – the CDC birth data warehouse. The stats below are based on the latest CDC data set, a 3.2 GB file containing natality information on the 4.26 million births registered in the US in 2008.

Some Background

First, some background info that I recently learned. At the start of the pregnancy you have a due date – when the baby is most likely to be born, based on when the doctor estimates the baby was conceived. Once the baby arrives, you can translate this date into an estimate of gestation, the number of days or weeks prego, by counting back to the estimated date of conception.

Stay with me.

The standard initial due date estimate is 280 days from the last menstrual period (LMP; ask your wife if you’re confused), or about 266 days from conception. This estimate is sometimes adjusted based on ultrasounds and such, but it’s typically close to 40/38 weeks.

So – we’re interested in the average gestation for women in the US and the variability around that average. The average, 38 weeks, is what they tell us at the early prenatal visits. The variability is key, as it will tell us the likelihood of the 38 for a randomly selected case, i.e, for our next kid.

The Stats

The plot above shows the adjusted gestation distribution for single births, in percentages. And the table below contains the mean, standard deviation, skewness, kurtosis, and count, for the adjusted and LMP gestations in 2008. I removed extreme outliers, flagged records, and missing data, which brought the counts down to under 4 million. Note that the adjusted estimates are much more accurate.

Some Gestation Stats
Estimate Mean SD Skew Kurtosis N
Adjusted 38.59 1.94 -3.21 22.61 3665402
LMP 38.73 2.37 -1.77 12.82 3672562

The take home message: due date margins are like the big stretchy waist bands on maternity pants. Only 75% of expectant moms have their baby within 10 days of the standard due date; 85% fall between weeks 37 and 40, making a huge 28-day margin. Plan accordingly.

By the way: 4.26 million births? That’s 8 per minute!

How Bad Would Another Kid Be?

new kid difficulty functionOccasionally people ask us what it’s like to go from n to n + 1 kids. The occasion is a couple, with one fewer kid than us, considering having another, which they’re afraid may be impractical and illogical, maybe even irresponsible. The simple answer is, it’s not as bad as going from n – 1 to n.

Mathematically, the more kids you have the easier it is to increment because you’re adding a difficulty factor of 1/n. From 0 to 1 you’re increasing by an impossible, infinite amount, 1/0; from 1 to 2, by 100%; from 2 to 3, by 50%; etc. So number 1 is a dramatic shock, but the proportional increase gets smaller the more you add.

That’s what people like to hear. It makes sense, and it sounds feasible. Keep in mind, the main assumption of this model is that your next kid will be of similar difficulty. Instead, kids usually differ in temperament, where one is an angel and the next is their alter ego or, worse, their arch nemesis. Just when you’ve got things under control with n kids, changing diapers one-handed, the nth + 1 shows up and you’re changing diapers no-handed. Chaos. Anarchy. Then you figure it out again. Then you have to potty train, again.

So, overall, in the long run, on average, the next kid is easier than the last. If you can make it to n = 6 you’ll hardly notice the change.