The effects of hormone replacement therapy (HRT) on serum markers of bone and cartilage metabolism. (a) Effect of HRT on serum (S) levels of type I collagen C-telopeptide (CTX-I). (b) Effect of HRT on serum levels of cartilage oligomeric matrix protein (COMP). Values are the medians (horizontal line), interquartile ranges (box), and ranges (whiskers). Circles (outliers) represent cases with values between 1.5 and 3 box lengths, and boxes (extremes) represent values more than 3 box lengths from the upper or lower edge of the box. Statistical differences between the groups and within each group are given.