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.
When a frequency table is used, the variance can also be given by the formula: Where Æ is the frequency of each individual value and âÆ is the sum of the individual frequencies which is the same as n. For grouped or continuous data the same formula is used but the X value is taken to be mid-point of each group.here $ $ represents each of the $ $ data points, $ $ is the mean of the set of data points and $ $ is the number of data points in the data set. The standard deviation, $ $ , is the square root of the variance, $ $ :