In the U.S., doctors usually get suspicious when a PSA level is 4.0 ng/mL. But studies show that many men with levels well above 4.0 ng/mL do not have cancer. And many men with prostate cancer have PSA scores well below this level. There are a lot of ways to tweak the PSA test to try to get better results.
The Standard Deviation Formula. In this formula, x is the value of the mean, N is the sample size, and x i represents each data value from i=1 to i=N.. The â symbol indicates that you must add up the sum. (x 1 - x) 2 + (x 2 - x) 2 + (x 3 - x) 2 + (x 4 - x) 2 + (x 5 - x) 2. . . + (x N-x) 2.
The standard deviation calculation tells you how spread out the numbers are in your sample. To figure this out for your sample or data set, you will need to perform a few calculations first. You will need to find the mean and variance of your data before you can find the standard deviation.Variance is a measure of how far your data is clustered around the mean. Standard deviation is found by taking the square root of the variance of your sample.ather all of your data. You will need every number in your sample to calculate the mean. 1  The mean is the average of all your data points. 2  This is calculated by adding all of the numbers in your sample, then dividing this figure by the how many numbers there are in your sample (n).