Figure 1.

Age-related trajectories of (A) total testosterone, (B) measured bioavailable testosterone, and (C) sex hormone–biding glycoprotein over the life span in men. The black dots correspond to the sample raw data. For participants with repeated measures, connecting lines are used to show the observed longitudinal trends in hormonal levels within the same person. The thick red line represents the population average trajectory as a function of age which is estimated from the final generalized model using all the available data, whereas 95% confidence intervals, depicted as dashed red lines, show the precision of this estimate.