How many standard deviations below the mean bone-mineral density of a young-adult reference population define osteoporosis diagnostically?

A) 1.5
B) 2.5
C) 3.5
D) 4.5

Bone-mineral Density

A measure of the amount of minerals (mainly calcium) contained in a certain volume of bone, indicating bone strength and risk for osteoporosis.

Standard Deviations

A measure of the amount of variation or dispersion of a set of values from the mean.

Diagnostically

Pertaining to or conducive to the determination or analysis of a disease's nature and its differentiation from other conditions.