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February 14, 2005
Kids grow in spurts
Kids grow in spurts, with a little jump every few days. There's a cool paper by Chris Schmid and Emery Brown with some data on the daily growth of children.
The graphs in the paper show 100 to 150 days of height measurements on each of 6 children. There are multiple measurements per day, and the pattern appears pretty clear for most of the kids: steady periods alternating with quick jumps in height. The data also show variation among children in the patterns and frequencies of jumps.
Chris and Emery fit a hierarchical Bayesian model to estimate the patterns of growth, and do some posterior predictive checks of the fit of the model. The paper also has references to the controversy about this "saltatory growth" in biology.
Their models allow for an arbitrary number of continuous jumps, with the scale estimated from data. The model seems similar to the methods of Neelon, B. and Dunson, D. B. (2004), Bayesian isotonic regression and trend analysis, Biometrics 60, 398-406, which David Dunson spoke about last year at Columbia.
Posted by Andrew at February 14, 2005 12:47 AM