The 2000 Centers for Disease Control and Prevention growth charts: several insights after 8 years.

This paper explores three issues related to the 2000 Centers for Disease Control and Prevention growth charts. First, it clarifies the methods that were used to create the charts as it has become apparent that the smoothing techniques have been somewhat misunderstood. The techniques included smoothing-selected percentiles between and including the 3rd and 97th percentiles and then approximating these smoothed curves using a procedure to provide the transformation parameters, lambda, mu, and sigma. Only the selected percentiles were used in this process due to small sample sizes beyond these percentiles. Second, given the concern that the infant charts were created with relatively few data points in the first few months of life, it compares the original observed percentiles with percentiles that include newly available US national data for the first few months of life. Third, it discusses the issues that arise if a 99th percentile is extrapolated based on the lambda, mu, and sigma parameters. The 99th percentile of the body mass index-for-age chart has been recommended to identify extremely obese children, yet the 97th percentile is the highest available percentile on the Centers for Disease Control and Prevention growth charts.