# Standard Deviation

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**Objectives**
By the end of this lesson you should be able to:

- distinguish between discrete and continuous data.
- calculate the variance for a given set of discrete data.

**Prerequisites**
You should ensure that you have writing material and that you understand *mean, frequency and sum* as they are used in statistics.
**Lesson**
Calculation of variances
For discrete variables, variance is calculated using the formula:

Where 'X' are the individual scores,is the mean of the data set and 'n' is the number of values in the data set.