Baby research: where do percentiles come from?
Posted by Jesse Rodgers on October 20, 2007 at 05:43 PM
Addison (my son) had his 9-month visit to the doctor this past week. All things are good, he is developing quickly, healthy, etc. But when referencing the baby height/weight chart the nurse found he was 25th percentile in weight, 75th or so in height. Concerned for his weight meant a friendly lecture from the nurse and an order to increase the fat in Addison’s diet. Keep in mind, this kid has more energy than anything I have ever seen. If he is awake he is moving and/or making noise.
So my wife comes home, thinks about it, and then last night found a paper explaining the chart our doctor’s office uses. As it turns out the research they use is from one town in the mid-west US and has bottle fed babies. Breast fed babies deviate significantly and negatively, especially those from other parts of the world. So the chart’s data source is flawed yet modern nurses and doctors follow it.
I wonder where the obesity problem starts? ;) Lesson of the day, if you are handed facts and you are not comfortable with them always do a little research. The web is really handy for that.
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My daughter was <50% at that age and is now following the curve around 40%. Our doc was never worried and neither were we. What’s important is watching your child’s trend along his own line. I.e. if he’s 25% now, you don’t want him to be 10% at 12 months. Remember, only in Lake Wobegone are all the children above average. Someone has to be below average.
The percentile thing is absurd. My 8 year old twin boys are at about the 5th percentile in weight, and out run, out skateboard, out surf and out last any of their peers. They eat well, including primarily organic foods, and almost never eat “happy meals” or chicken nuggets. They drink milk and water instead of soda and gatorade.
The problem with the percentile charts is simple. The 50th percentile basically represents the middle of the population it is measuring. If that population is obese, the 50th percentile will actually be overweight.
If your child is active, healthy and happy, that says more than any chart can possibly say.
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