Guides
Growth chart guides
Four guides on the statistics and the measurement technique behind a growth chart, written to explain what the number is doing rather than what it means for a particular child. That reading belongs with your pediatrician, and these guides never attempt it.
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How to take a measurement at home that is worth plotting
Technique, not interpretation: how weight, length, standing height and head circumference are measured for a growth chart, and where the error creeps in at home.
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What a growth percentile actually means
A percentile is a position in a reference population, not a grade. Here is exactly what the number is measuring, where it comes from, and what it cannot tell you.
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Why the 10th percentile is a completely ordinary place to be
Ten percent of a healthy reference population sits at or below the 10th percentile, by construction. Here is the arithmetic of why the low bands are populated, and what the number does and does not tell you.
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Why the WHO and CDC growth charts differ, and why the switch happens at two
One is a prescriptive standard built from six countries, the other a descriptive US reference. The history explains the shape of both charts and the visible step at 24 months.
Then plot something on the percentile chart, or read the published parameter tables on the reference tables page.