SITAR - a useful instrument for growth curve analysis
Résumé
Background Growth curve analysis is a statistical issue in life course epidemiology. Height in puberty involves a growth spurt whose timing and intensity varies between individuals. Such data can be summarised with individual Preece-Baines (PB) curves, and their five parameters then related to earlier exposures or later outcomes. But it involves fitting many curves. Methods We present an alternative SuperImposition by Translation And Rotation (SITAR) model, a shape invariant model with a single fitted curve. Curves for individuals are matched to the mean curve by shifting their curve up-down (representing differences in mean size) and left-right (for differences in growth tempo), and the age scale is also shrunk or stretched to indicate how fast time passes in the individual (i.e. velocity). These three parameters per individual are estimated as random effects while fitting the curve. The outcome is a mean curve plus triplets of parameters per individual (size, tempo and velocity) that summarise the individual growth patterns. Data: heights for Christ's Hospital School (CHS) boys aged 9-19 years (N=3245, n=129 508), and Turner Syndrome (TS) girls aged 9-18 years from the UK Turner Study (N=105, n=1321). Results The SITAR model explained 99% of the variance in both datasets (RSD 6-7 mm), matching the fit of individually-fitted PB curves. In CHS, growth tempo was associated with IGF-1 measured 50 years later (P=0.01, N=1009). For the TS girls randomised to receive oxandrolone from 9 years, velocity was substantially increased compared to placebo (P=10-8). Conclusions The SITAR growth curve model is a useful epidemiological instrument for the analysis of height in puberty.
Origine : Fichiers produits par l'(les) auteur(s)
Loading...