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.
Sample Standard Deviation. A standard deviation of a sample estimates the standard deviation of a population based on a random sample. The sample standard deviation, unlike the population standard deviation, is a statistic that measures the dispersion of the data around the sample mean.tandard deviation refers to the amount of dispersion in a given data set. Researchers calculate the standard deviation of a data set by taking the square root of the variance, and the numerical result is indicated by the letter S. They use the term âvarianceâ to describe the extent of the data spread.