N

- k

with yi, the height at x; y., the value of the fitted curve at x; N, the number of height measurements; and k, the number of parameters in the model (five in the case of PB1). It is generally accepted that a fitted curve adequately describes the growth

Age, years figure 3-4 Growth in height of a girl (no. 29) between 3 and 18 years old. The upper part shows a plot of the height-for-age data together with the Preece-Baines model 1, while the lower part shows the yearly increments in weight with the first derivative of the fitted curve. (From the Belgian Growth Study of the Normal Child.)

Age, years figure 3-4 Growth in height of a girl (no. 29) between 3 and 18 years old. The upper part shows a plot of the height-for-age data together with the Preece-Baines model 1, while the lower part shows the yearly increments in weight with the first derivative of the fitted curve. (From the Belgian Growth Study of the Normal Child.)

data if the standard error of estimate is of the same order of magnitude as the measurement error of the trait under consideration (typically 0.5 cm for stature during childhood and adolescence). Systematic bias can be estimated as the test runs.23 Large values of the standard error of estimate and systematic bias may, among others, occur with

• Low-precision data (large measurement error, inexperienced measurers, large intermeasurer variation, inadequate measuring devices, and so on).

table 3-1 Function Parameters and Biological Parameters Obtained by Fitting Preece-Baines Model 1 to the Height Data of Girl No. 29 (taken from the Belgian Growth Study of the Normal Child1)

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