After completion of this chapter, students will be able to:

- know more about the statistics.
- solve the problems related to mean, median and standard deviation.

Mean deviation The average of the absolute values of the deviation of each item from mean, median or mode is known as a mean deviation. Standard deviation Standard deviation is the positive square root of the arithmetic mean of the square of deviations of given data taken from the mean.

**Standard Deviation**

Standard deviation is the position square root of the arithmetic mean of the squares of the deviations of the given observation from their arithmetic mean.

**Merits and Demerits of Standard Deviation**

**Merits**

- The value of standard deviation is based on each and every item of the data.
- It is free from those defects with which other methods like range, quartile deviation, mean deviation suffer.
- It is less affected by fluctuations of sampling.

**Demerits**

- As compared to the measure, it is somewhat more difficult to understand and compute.
- Its value is unduly affected by extreme observations.