In a normally distributed fibromyalgia functional loss score where 33 is two standard deviations below the mean and 55 is two standard deviations above the mean, what percentage of subjects scores between 33 and 55?

In a normally distributed fibromyalgia functional loss score where 33 is two standard deviations below the mean and 55 is two standard deviations above the mean, what percentage of subjects scores between 33 and 55?

• A. 95%
• B. 15%
• C. 50%
• D. 6.67%

Answer: (A)

The main idea is the empirical rule for normal distributions: about 95% of values fall within two standard deviations of the mean. Since 33 is two standard deviations below the mean and 55 is two standard deviations above the mean, the scores between 33 and 55 capture roughly 95% of subjects. The remaining 5% lie beyond these bounds (about 2.5% below 33 and 2.5% above 55).

The main idea is the empirical rule for normal distributions: about 95% of values fall within two standard deviations of the mean. Since 33 is two standard deviations below the mean and 55 is two standard deviations above the mean, the scores between 33 and 55 capture roughly 95% of subjects. The remaining 5% lie beyond these bounds (about 2.5% below 33 and 2.5% above 55).