Osteoporosis is a condition in which the bones become brittle due to loss of min

Question

Osteoporosis is a condition in which the bones become brittle due to loss of minerals. To diagnose osteoporosis, an elaborate apparatus measures bone mineral density (BMD). BMD is usually reported in standardized form. The standardization is based on a population of healthy young adults. The World Health Organization (WHO) criterion for osteoporosis is a BMD 2.5 standard deviations below the mean for young adults. BMD measurements in a population of people similar in age and sex roughly follow a Normal distribution. What percent ( 0.1) of healthy young adults have osteoporosis by the WHO criterion? Women aged 70 to 79 are of course not young adults. The mean BMD in this age is about ?1.9 on the standard scale for young adults. Suppose that the standard deviation is the same as for young adults. What percent ( 0.1) of this older population has osteoporosis?

Explanation / Answer

Formula: X-mean/SD Convert your answers to percents using Table A. Part 1: (641-534)/110 = .9727 about 83.5% Part 2: (25.8-16.9)/6.4 = 1.3906 about 92% Gerald Wins! Use table A as well. SD=Z So the percent of healthy young adults that have osteoporosis is 0.6% Think of -2 as 0 for the second part, the difference between -2.0 and -2.5 is -.5, this will be your new Z-score. Table A gives you about 31%

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