Fig. 1

Longitudinal modeling of aBMD and BMC. a Bone Mineral Density in Childhood Study (BMDCS) was a multi-ethnic longitudinal prospective study of healthy children and adolescents collected over 7 years at 5 clinical sites across the USA to establish national reference curves for bone density (study visit details are given in Additional file 1: Table S1). b The three SITAR model parameters are a-size, representing an up-down shift on the y-axis for an individual compared to the population mean; b-timing, representing an earlier-later shift on the x-axis compared to the population mean; and c-velocity, corresponding to differences in the rate of bone accrual. c Six skeletal sites were assessed (total body less head, 1/3 distal radius, lumbar spine, femoral neck, total hip, and skull) for bone mineral density (g/cm²) and content (g). Mean SITAR curves for aBMD and BMC by sex and ancestry are shown in Additional file 2: Fig. S1