An injury to the vertebrae or discs in your neck can cause pain, numbness, or weakness in your shoulder, arm, wrist, or hand because the nerves that extend out from between the neck provide sensation and allow for movement in these areas.
Variance is defined as the mean of the squares of the individual differences from the mean. To calculate the variance within a set of data, you would first calculate the mean by adding up all of your data points and then dividing the total by the number of data points being used.
The derivation starts with a recognition that the variance of the difference between independent random variables is equal to the sum of the individual variances. Thus, Ï 2 d = Ï 2 (x1 - x2) = Ï 2 x1 + Ï 2 x2.