Refer to Exercise 17. Judy’s friend Mary also had the bone density in her hip measured using DEXA. Mary is 35 years old. Her bone density is also reported as 948 g/cm², but her standardized score is z=0.50. The mean bone density in the hip for the reference population of 35-year-old women is 944 grams/cm².

a. Whose bones are healthier for her age: Judy’s or Mary’s? Justify your answer.

b. Calculate the standard deviation of the bone density in Mary’s reference population. How does this compare with your answer to Exercise 17(b)? Are you surprised?

Exercise 17.

Individuals with low bone density (osteoporosis) have a high risk of broken bones (fractures). Physicians who are concerned about low bone density in patients can refer them for specialized testing. Currently, the most common method for testing bone density is dual energy X-ray absorptiometry (DEXA). The bone density results for a patient who undergoes a DEXA test usually are reported in grams per square centimeter (g/cm²) and in standardized units.

Judy, who is 25 years old, has her bone density measured using DEXA. Her results indicate bone density in the hip of 948 g/cm² and a standardized score of z=−1.45. The mean bone density in the hip is 956 g/cm² in the reference population of 25-year-old women like Judy.3