What is a standard deviation? What is variance?
The standard deviation is one way of describing the “scatter” of a distribution of scores—the degree to which the scores vary from the central tendency. These measures of scatter or dispersion are, like the concepts of central tendency described in the previous section, essential to understanding the T scales on which the MMPI instruments are based. The statistical formula for the standard deviation is somewhat complicated. Each score is subtracted from the mean to produce a deviation from the mean. Each of these deviations is squared. (A number is squared when the number is multiplied by itself. The square of 2—that is to say, 2 times 2—is 4; the square of 3—that is, 3 times 3—is 9; the square of 4 is 16.) These squared deviations are then added together into a total sum of squares. The total sum of squares is then divided by the number of scores. [Footnote: This is the formula for determining the variance or standard deviation in descriptive statistics. In inferential statistics, th
