Standard Deviation and Variance, a first look

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Standard deviation

The standard deviation is a measure of the spread of the data.  As with the mean it comes in a number of flavours.

• Standard deviation of the population

We use this when we know all the outcomes. For example if we have a census (asked everyone) instead of  a sample (asked some).

We have

${{\sigma }_{x}}=\sqrt{E({{(x-\bar{x})}^{2}})}=\sqrt{\frac{\sum{{{(x-\bar{x})}^{2}}}}{n}}$

I.e. the standard deviation is the square root of the expected value of the square of the difference between the values and the average.

• Under construction.

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Previous page : The Mean or AverageLast modified: Jan 3, 2017 @ 22:07