Plots height or length (in centimeters) based on the WHO growth charts for <= 2 years and the CDC growth charts for older than 2. For for the age range 0 to 3 years, recumbent length is used; for the 0 to 20 and 3 to 20 year ranges, standing height is used for ages greater or equal to 24 months. In the 0 to 20 years graph, these changes create a small "jog" at the 24 month point.
It should be noted that these charts are prescriptive rather than descriptive; they reflect what the National Center for Health Statistics and the World Health Organization think the distribution of weights in children ought to be, rather than what it is (see the original paper, 2000 CDC Growth Charts for the United States: Methods and Development, page 16, and the discussion from the CDC about changing to the WHO tables).
The height distribution for children with Down Syndrome is from Health Supervision for Children With Down Syndrome, PEDIATRICS Vol. 107 No. 2 February 2001, pp. 442-449.
Sex is determined by
sex=female. If neither is specified, then the percentiles are
"Heights" for < 24 months are all recumbent lengths; heights for >= 36 months are standing heights. If the parameter
recumbent=yes is set, then the 24-36 month range used recumbent lengths; otherwise it uses standing heights.
down=yes to get the Down Syndrome graphs.
The 3 percentile line is actually 2.3% and the 97 percentile line is actually 97.7% for age <= 2 years; that's just the way the WHO published it.