Sigma is a statistical term that refers to standard deviation, which is a

measure of variability or error in data.

In addition to the 31-point range in quarterly approval ratings, another

measure of variability, statistical standard deviation, is 9 points for Hispanics, compared with 6 points for all U.

Although a measure of the central tendency of a distribution of measurements and a corresponding

measure of variability are not quite independent of each other--either mathematically or empirically (the standard deviation is, for example, most often positively related to the mean)--a

measure of variability may provide useful information over and above that provided by the central measure, as demonstrated, for example, by recent research on performance as related to aging (e.

With a distribution-based approach, clinical importance is evaluated by comparing the size of the effect of intervention to some

measure of variability, such as the between-person variability in outcomes or the variability associated with repeated measures of the outcome.

The next step is to incorporate this

measure of variability into the optimization problem.

In statistics, the lower-case Greek letter "sigma" ([sigma]) is used to indicate the standard deviation, a

measure of variability.

Treasury bills have the lowest average return as well as the lowest value of the

measure of variability of return--the standard deviation.

A

measure of variability known as the Z' factor is routinely in the 0.

A robust

measure of variability is the Inter Quartile range (IQR) which is plotted (along with a smooth of the same) in Figure 3A.

14)Other robustness checks include estimation by ordinary least squares, and use of the industry variance, rather than the covariance with GNP, as the

measure of variability.