COVAR function
Returns covariance, the average of the products of deviations for each data point pair in two data sets.
Use covariance to determine the relationship between two data sets. For example, you can examine whether greater income accompanies greater levels of education.
Important This function has been replaced with one or more new functions that may provide improved accuracy and whose names better reflect their usage. Although this function is still available for backward compatibility, you should consider using the new functions from now on, because this function may not be available in future versions of Excel.
For more information about the new functions, see COVARIANCE.P function and COVARIANCE.S function.
Syntax
COVAR(array1,array2)
The COVAR function syntax has the following arguments:

Array1 Required. The first cell range of integers.

Array2 Required. The second cell range of integers.
Remarks

The arguments must either be numbers or be names, arrays, or references that contain numbers.

If an array or reference argument contains text, logical values, or empty cells, those values are ignored; however, cells with the value zero are included.

If array1 and array2 have different numbers of data points, COVAR returns the #N/A error value.

If either array1 or array2 is empty, COVAR returns the #DIV/0! error value.

The covariance is:
where
are the sample means AVERAGE(array1) and AVERAGE(array2), and n is the sample size.
Example
The example may be easier to understand if you copy it to a blank worksheet.
How to copy an example

Create a blank workbook or worksheet.

Select the example in the Help topic.
Note Do not select the row or column headers.
Figure 1: Selecting an example from Help

Press CTRL+C.

In the worksheet, select cell A1, and press CTRL+V.

To switch between viewing the results and viewing the formulas that return the results, press CTRL+` (grave accent), or on the Formulas tab, in the Formula Auditing group, click the Show Formulas button.

