Standard normal table z score P908/7/2023 ![]() ![]() However, in this case we want to start with a 90% probability and find the value of "X" that represents it. ![]() Previously we started with a particular "X" and used the table to find the probability. ![]() To compute the 90 th percentile, we use the formula X=μ + Zσ, and we will use the standard normal distribution table, except that we will work in the opposite direction. The 90 th percentile is the BMI that holds 90% of the BMIs below it and 10% above it, as illustrated in the figure below. What is the 90 th percentile of BMI for men? The mean BMI for women aged 60 the mean is 28 with a standard deviation of 7.The mean BMI for men aged 60 is 29 with a standard deviation of 6.Where μ is the mean and σ is the standard deviation of the variable X, and Z is the value from the standard normal distribution for the desired percentile. The formula below is used to compute percentiles of a normal distribution. In some instances it may be of interest to compute other percentiles, for example the 5 th or 95 th. For example, the median is the 50 th percentile, the first quartile is the 25 th percentile, and the third quartile is the 75 th percentile. The standard normal distribution can also be useful for computing percentiles. ![]()
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