A measure of the variation around the estimate of the mean.
The standard deviation is a statistic that lets you know how tightly all the subjects are clustered around the mean in a set of data. A single standard deviation away from the mean in either of the directions accounts for somewhere around 68 % of data. If two standard deviations are away from the mean, it accounts for around 95% of data. If three standard deviations are away it accounts for 99% of the data.
1) The total range of variation in the dataset is called RANGE.
3) A measure of the variation around the estimate of the mean is SEM (STANDARD ERROR OF THE MEAN).
4) The most common value observed (highest frequency) is MODE.