A mixed effects model to estimate timing and intensity of pubertal growth from height and secondary sexual characteristics

AIM To estimate and compare pubertal growth timing and intensity in height, Tanner stage markers and testis volume. SUBJECTS AND METHODS Data on height, genital stage, breast stage and pubic hair stage, testis volume and menarche in 103 boys and 74 girls from the Edinburgh Longitudinal Growth Study were analysed. The SITAR model for height and a novel mixed effects logistic model for Tanner stage and testis volume provided estimates of peak velocity (PV, intensity) and age at peak velocity (APV, timing), both overall (from fixed effects) and for individuals (random effects). RESULTS Based on the six markers, mean APV was 13.0-14.0 years in boys and 12.0-13.1 years in girls, with between-subject standard deviations of ~1 year. PV for height was 8-9 cm/year by sex and for testis volume 6 ml/year, while Tanner stage increased by 1.2-1.8 stages per year at its peak. The correlations across markers for APV were 0.6-0.8 for boys and 0.8-0.92 for girls, very significantly higher for girls (p = 0.005). Correlations for PV were lower, -0.2-0.6. CONCLUSIONS The mixed effects models perform well in estimating timing and intensity in individuals across several puberty markers. Age at peak velocity correlates highly across markers, but peak velocity less so.