Variance and standard deviation of data in data mining

What is data variance and standard deviation?

Different values in the data set can be spread here and there from the mean. Variance tells us that how far away are the values from the mean.

Standard deviation is the square root of the variance.

Low standard deviation

Low standard deviation tells us that fewer numbers are far away from the mean.

High standard deviation

High standard deviation tells us that more numbers are far away from the mean.

The formula to calculate the standard deviation of sample and population

standard deviation formula

Figure: standard deviation formula

How to calculate variance and standard deviation of a population data?

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z score normalization standard deviation

Figure:  standard deviation

Mean = 13.25

Variance = 21.6

Standard deviation = 4.6

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