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Fig. 1 | BMC Medical Research Methodology

Fig. 1

From: Using linear and natural cubic splines, SITAR, and latent trajectory models to characterise nonlinear longitudinal growth trajectories in cohort studies

Fig. 1

Example illustrating the limitations of using polynomial functions to approximate a nonlinear growth trajectory. Coloured lines represent predicted trajectories from LME models with age as (a) linear term and as (b) quadratic polynomial and (c) cubic polynomial. Points display weight measurements taken from 70 females in the Berkeley Child Guidance Study. Dataset was originally provided as an appendix to the book by Tuddenham and Snyder (1954). The data for this example were taken from the freely accessible ‘Berkeley’ dataset provided with the ‘sitar’ package [15]

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