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SITAR--a useful instrument for growth curve analysis.

Cole TJ, Donaldson MD, Ben-Shlomo Y - Int J Epidemiol (2010)

Bottom Line: In CHS, growth tempo was associated with insulin-like growth factor-1 measured 50 years later (P = 0.01, N = 1009).For the girls with TS randomized to receive oxandrolone from 9 years, velocity was substantially increased compared with placebo (P = 10(-8)).The SITAR growth curve model is a useful epidemiological instrument for the analysis of height in puberty.

View Article: PubMed Central - PubMed

Affiliation: MRC Centre of Epidemiology for Child Health, UCL Institute of Child Health, London, UK. tim.cole@ich.ucl.ac.uk

ABSTRACT

Background: Growth curve analysis is a statistical issue in life course epidemiology. Height in puberty involves a growth spurt, the timing and intensity of which varies between individuals. Such data can be summarized 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 summarize the individual growth patterns. The data are heights for Christ's Hospital School (CHS) boys aged 9-19 years (N = 3245, n = 129,508), and girls with Turner syndrome (TS) 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 [residual standard deviation (RSD) 6-7 mm], matching the fit of individually-fitted PB curves. In CHS, growth tempo was associated with insulin-like growth factor-1 measured 50 years later (P = 0.01, N = 1009). For the girls with TS randomized to receive oxandrolone from 9 years, velocity was substantially increased compared with placebo (P = 10(-8)).

Conclusions: The SITAR growth curve model is a useful epidemiological instrument for the analysis of height in puberty.

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Related in: MedlinePlus

Turner Study data. Left: 105 height growth curves and 1321 heights from 9 to 19 years as randomized (oxandrolone red solid lines, placebo blue dashed lines). Right: the same curves after SITAR adjustment
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Figure 4: Turner Study data. Left: 105 height growth curves and 1321 heights from 9 to 19 years as randomized (oxandrolone red solid lines, placebo blue dashed lines). Right: the same curves after SITAR adjustment

Mentions: Figure 4 shows the individual raw and SITAR-adjusted growth curves for the TS cohort, colour coded by trial arm. The raw RSD is 5.9 cm, which shrinks to 0.6 cm on adjustment for the three parameters. Thus again 99% of the variance is explained by the SITAR model, and the remaining variability matches that of the PB curve. On this basis it can be argued that the three SITAR parameters explain all the differences in growth between individuals, so that they constitute a parsimonious summary of the individual growth curves.Figure 4


SITAR--a useful instrument for growth curve analysis.

Cole TJ, Donaldson MD, Ben-Shlomo Y - Int J Epidemiol (2010)

Turner Study data. Left: 105 height growth curves and 1321 heights from 9 to 19 years as randomized (oxandrolone red solid lines, placebo blue dashed lines). Right: the same curves after SITAR adjustment
© Copyright Policy - creative-commons
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC2992626&req=5

Figure 4: Turner Study data. Left: 105 height growth curves and 1321 heights from 9 to 19 years as randomized (oxandrolone red solid lines, placebo blue dashed lines). Right: the same curves after SITAR adjustment
Mentions: Figure 4 shows the individual raw and SITAR-adjusted growth curves for the TS cohort, colour coded by trial arm. The raw RSD is 5.9 cm, which shrinks to 0.6 cm on adjustment for the three parameters. Thus again 99% of the variance is explained by the SITAR model, and the remaining variability matches that of the PB curve. On this basis it can be argued that the three SITAR parameters explain all the differences in growth between individuals, so that they constitute a parsimonious summary of the individual growth curves.Figure 4

Bottom Line: In CHS, growth tempo was associated with insulin-like growth factor-1 measured 50 years later (P = 0.01, N = 1009).For the girls with TS randomized to receive oxandrolone from 9 years, velocity was substantially increased compared with placebo (P = 10(-8)).The SITAR growth curve model is a useful epidemiological instrument for the analysis of height in puberty.

View Article: PubMed Central - PubMed

Affiliation: MRC Centre of Epidemiology for Child Health, UCL Institute of Child Health, London, UK. tim.cole@ich.ucl.ac.uk

ABSTRACT

Background: Growth curve analysis is a statistical issue in life course epidemiology. Height in puberty involves a growth spurt, the timing and intensity of which varies between individuals. Such data can be summarized 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 summarize the individual growth patterns. The data are heights for Christ's Hospital School (CHS) boys aged 9-19 years (N = 3245, n = 129,508), and girls with Turner syndrome (TS) 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 [residual standard deviation (RSD) 6-7 mm], matching the fit of individually-fitted PB curves. In CHS, growth tempo was associated with insulin-like growth factor-1 measured 50 years later (P = 0.01, N = 1009). For the girls with TS randomized to receive oxandrolone from 9 years, velocity was substantially increased compared with placebo (P = 10(-8)).

Conclusions: The SITAR growth curve model is a useful epidemiological instrument for the analysis of height in puberty.

Show MeSH
Related in: MedlinePlus