# stats 110

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Dispersion
Dispersion gives idea of spread of data from the central value say mean.

Deviation.
Deviation is the difference between a observation and some reference value. Observation value is usually represented by X bar.
Deviation of x from some value A is X — A.
Deviation from mean is X – X

Absolute deviation
When deviation is always taken as positive irrespective of its sign, it is called as absolute deviation. It is represented as | X – X |

Mean deviation
It is sum of absolute deviations from mean divided by total number of observations. See chapter 2 for examples.

Standard Deviation
It is square root of sum of squares of mean deviation divided by total number of observations. See chapter 2 for examples.

Variance
Variance is square of standard deviation. See chapter 2 for examples.

Quartile deviation
It is the difference between the third quartile and first quartile divided by 2. It is also called as semi quartile range. See chapter 2 for examples.

Inter Quartile range
It is the difference between the third quartile and first quartile. See chapter 2 for examples.

Range
Range is the difference between the largest value and the smallest value of the data set. See chapter 2 for examples.