Monday, January 14, 2013

The Measurement of Babies

Sorry, for anyone who may be bored of it, but I've got to post another science/baby post.  I was planning to (finally) write about our programming language semantics paper that came out a few weeks ago, but I'm deferring it again because I'm just more psyched to write about baby-metrics right now.  So you'll just have to wait another week before you hear about the most symbol-dense paper I have yet published.

As anyone who is a parent surely knows, tracking the progress of one's child can become a minor obsession.  There are just so many resources available that will happily tell you what to expect at each month, what's normal, what's not, etc.  I've fought back against this by embracing the Dr. Spock approach, which basically boils down to: "First, enjoy your baby.  Second, learn from your baby."

Still, there are a few things that you can't help being informed of at regular intervals, like height and weight percentiles.  Harriet had a rough start, and in her first few days dipped down near the 5th percentile weight line (the level at which Medicine Becomes Concerned), so we are perhaps even more aware of those than we might be otherwise.  She caught up well, so no worries.  But now in the long interval between her 4-month and 6-month checkups (hah!), we started wondering whether our seemingly always ravenous little girl was going overboard on the other side, and ended up looking up height and weight charts.

No problems, and I basically forgot about it until today, when Harriet was playing with a carpentry level (another fine household object toy), and we realized she was taller than it---more than 30 inches, which according to my chart was well above 95th percentile for her age! Well, nothing gets a couple of scientists going like an unexpected result... out came the hypotheses.

Could the chart be wrong? Careful inspection found a CDC watermark and url blurred in the bottom of the image, which led to the original rather trustworthy source.  There is even, delightfully, a complete methods paper, which I pulled up and started going through, while the subject of the investigation shifted her attention to a joint manual/oral assay of the texture of socks (Fabric Sciences 102).

Yes, our baby is apparently a long, trim little girl, according to primary sources.  But what was their statistical data pool?  Do we know if there are ethnic variations?  What would that say about an F1 hybrid of Anglo-Saxon and Bengali?  Are there epigenetic effects linked to immigration to a high-nutrition country?

The CDC report itself didn't have enough data for studying the extremas of different ethnicities: although their birth statistics were massive, the infant-to-toddler range only comes from a few tens of thousands of data points, and the data is all at least 15 years old, when the country was significantly more homogeneous.  Their discussion and citations on the matter, though, argue very solidly that ethnicity has pretty much null effect compared to nutrition---it looks like there's been a lot of research on the matter, and especially regarding Mexican-Americans.  I haven't been able to find any references specifically investigating biracial children yet... but we didn't dig very deeply, since a real baby has priority over a metrized baby-model.

And the conclusion is... we have a long, trim little girl, and her parents can just leave the rest be, unless we want to have fun telling Just-So stories.

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