The SITAR method of growth curve analysis for growth assessment in translational medicine and life course epidemiology

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The pattern of growth in individual children, as represented by their growth curve of successive measurements (e.g. weight or height) plotted against age, may be informative about their circumstances at earlier ages, or conversely it may predict their risk of disease later in life, for example heart disease, stroke or type 2 diabetes. To investigate this it is necessary to summarise the shape of each individual's growth curve in a simple way, so that its shape can be related to their earlier or later experiences. The SITAR method of growth curve analysis is a novel approach that does just this - it summarises each individual growth curve in just three numbers, reflecting respectively their size (i.e. tall or short, heavy or light, as compared to others), their growth tempo (i.e. whether they are relatively mature or delayed in their timing of growth, e.g. age of menarche in girls), and velocity (how fast they are growing compared to others, e.g. in puberty). In addition SITAR estimates a smooth average growth curve against which each individual's growth can be compared. The surprising thing is that this model explains nearly all of the variability in growth between individuals, so that their size, tempo and velocity can be viewed as a complete summary of their growth pattern. Put another way, when adjusted for size, tempo and velocity all their growth curves are the same. It is then simple to relate the values of size, tempo and velocity in individuals to their earlier or later experiences, and to look for links between them.