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.
For an unbiased estimate, the sum of the signed deviations across the entire set of all observations from the overall sample mean is always zero, and the expected, mean, or average deviation is also zero; conversely, a nonzero average deviation quantifies the bias exhibited by the estimate.tatistics of the distribution of deviations are used as measures of statistical dispersion. 1  Standard deviation is the frequently used measure of dispersion: it uses squared deviations, and has desirable properties, but is not robust.