Cross-sectional measurements of the percentage of free IGF-I to total IGF-I in the study population. Age distribution of the percentage of free IGF-I to total IGF-I levels in males (A) and females (B) are represented respectively. The curves of the 5th, 10th, 25th, 50th, 75th, 90th, and 95th percentiles of the percentage of free IGF-I to total IGF-I level calculated by BCT method are displayed.