Question

A ferritin test is a popular test to measure a person’s current iron stores. in women, ferritin is normally distributed with a mean of 89 ng/ml plus a standard deviation of 23 ng/ml. what is the probability that a woman has a ferritin value of 100 or less?

Answer 1

Given:
μ = 89 ng/ml, population mean
σ = 23 ng/ml, population standard deviation

Random variable, x = 100
To test P(x < 100), calculate the z-score.
 z = (x-μ)/σ = (100 - 89)/23 = 0.4783

From standard tables, obtain
P(x < 100) = 0.6838 = 68.4%

Answer: 68.4%