Standard Deviation
Standard Deviation is the square root of the variance of the random variable or probability distribution. Variance in itself is an excellent measure of variability and range; a larger variance reflects a greater spread in the data set.
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Absolute deviation of an element of a data set is the absolute difference between that element and a given point. Typically the deviation is reckoned from the central value, being construed as some type of average, most often the median or sometimes the mean of the data-set.
Average absolute deviation
The average absolute deviation of a data set is the average of the absolute deviations. Note here we are talking about averaging the absolute deviation calculated using the mean, median, mode, or some another measure of central tendency.
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