Standard Deviation is a statistical measure, that is closely linked to Variance. Both measures are commonly used across a set of values, to identify the amount that the values differ (or deviate) from the average value.
When your data set is a sample of a population, (rather than an entire population), you should use a slightly modified form of the Standard Deviation, known as the Sample Standard Deviation. The equation for this is:
The Excel STDEV.S function calculates the sample standard deviation of a supplied set of values.
The function is new in Excel 2010 and so is not available in earlier versions of Excel. However, the Stdev.S function is simply a new version of the Stdev function that is available in earlier versions of Excel.
The format of the Stdev.S function is:
Note that the Stdev.S function is used when calculating the standard deviation for a sample of a population (eg. if your data set records the individual heights of a sample of UK males). If you are calculating the standard deviation of an entire population, you should use the Stdev.P function.
Imagine you wanted to find out the standard deviation of the heights of adult males in London. It is not possible to measure the height of all males, but you could take a sample of the population and measure their heights.
The above example spreadsheet on the right stores the measurements (in cm) of 3,000 adult males. The measured heights are stored in cells B3 - B1002, D3 - D1002 and F3 - F1002.
As shown in cell H3, the Stdev.S function calculates the standard deviation in the measured heights to be 5.4 cm.
In the example above, the arguments to the Stdev.S function are input as 3 cell ranges. However, you can also input figures directly, as individual numbers or number arrays.
For example, if you wanted to include two further heights, of 176cm and 177cm into the sample, you could add these directly into the above function as follows:
Further information and examples of the Excel Stdev.S function can be found on the Microsoft Office website.
If you get an error from the Excel Stdev.S function this is likely to be one of the following:
|#DIV/0!||-||(Note that text representations of numbers, that are supplied as a part of an array, are not interpreted as numeric values by the Stdev.S function)|
|#VALUE!||-||Occurs if any values that are supplied directly to the Stdev.S function are text values that cannot be interpreted as numeric values.|