The standard deviation is a descriptive statistic. This particular measurement tells us about the dispersion of a set of data. In other words, it tells us how spread out a set of data is. Just like using many other formulas in statistics, the calculation of a standard deviation is a fairly tedious process to do by hand. Fortunately statistical software speeds up this calculation considerably.

There are many software packages that do statistical calculations.

One of the most readily accessible programs is Microsoft Excel. Although we could use a step by step process and use the formula for a standard deviation for our calculation, it is possible to simply enter all of our data into one function in order to find a standard deviation. We will see how to calculate a sample standard deviation in Excel.

### Populations and Samples

Before moving on to the specific commands used to calculate a standard deviation, it is important to distinguish between a population and a sample. A population is the set of every individual being studied. A sample is a subset of a population. The difference between these two concepts means the difference in how a standard deviation is calculated.

### Standard Deviation in Excel

To use Excel to determine the sample standard deviation of a set of quantitative data, type these numbers into a group of adjacent cells in a spreadsheet.

In an empty cell type what is in the quotation marks "=STDEV.S( ". Following this type the location of the cells where the data is and then close the parentheses with " ) ". This can alternatively be done by use of the following procedure. If our data is located in cells A2 to A10, then (omitting the quotation marks) "=STDEV.S(A2:A10)" will obtain the sample standard deviation ofthe entries in cells A2 to A10.

Rather than typing the location of the cells where our data is located, we can use a different method. This involves typing the first half of the formula "=STDEV.S( ", and clicking on the first cell where the data is located. A colored box will appear around the cell that we have selected. We then drag the mouse until we have selected all of the cells that contain our data. We finish this by closing the parentheses.

### Cautions

There a few cautions that must be made in using Excel for this calculation. We need to make sure that we do not mix up out functions. The Excel formula STDEV.S closely esembles STDEV.P. The former is typically the necessary formula for our calculations, as it is used when our data is a sample from a population. In the event that our data constitutes the entire population being studied, then we would want to use STDEV.P.

Another thing that we must be careful about concerns the number of data values. Excel is limited by the number of values that can be entered into the standard deviation function. All of the cells that we use for our calculation must be numerical. We must be sure that error cells and cells with text in them are not entered into the standard deviation formula.