Quantitative ultrasound is a cheaper but less accurate alternative to the standard technique of measuring this quantity. Drugs used to increase this quantity include alendronate and zoledronate. Age, height, weight, TBS, and this quantity are the main inputs of the FRAX tool. Jean Lobstein described a condition in which this quantity is low (15[1])that often results in blue sclerae. Since sex hormones increase this quantity, a decrease in this quantity is a common side effect of (*) puberty blockers and androgen (10[1])deprivation therapy. This quantity is typically measured with DEXA (10[1])scans. Inability to form type I collagen leads to this quantity being low in a condition partially called "imperfecta." This quantity is increased by bisphosphonates and lowered by parathyroid hormone. For 10 points, name this quantity that is low in people with rickets and osteoporosis. ■END■