The Variance is a statistical measure, that is commonly used across a set of values, to identify the amount that the values vary 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 Variance, known as the Sample Variance. The equation for this is:
where,
The Excel VARA function calculates the sample variance of a supplied set of values.
The syntax of the function is:
Where the number arguments are values or arrays of values that provide a minimum of 2 numeric values to the function. You can enter up to 255 number arguments to the Vara function in current versions of Excel (2007 and later), but you can only enter up to 30 number arguments in Excel 2003.
Note that the Vara function is used when calculating the variance for a sample of a population (e.g. if your data set records the individual heights of a sample of UK males). If you are calculating the variance for an entire population, you should use the Excel Varpa function.
The Excel Vara function is very similar to the Excel Var function, in that both functions calculate the sample variance of a supplied set of values.
The difference between these two functions applies when an array of values, containing text or logical values is supplied to the function. In this case, the Var function ignores the text and logical values, whereas the Vara function assigns the value 0 to text and the values 1 or 0 to logical values.
The rules for this are shown in the table below, compared to the rules for the Var function.
VAR Function  VARA Function  

Logical values or text (including text representations of numbers), typed directly into the list of arguments  ARE counted (TRUE=1, FALSE=0)  ARE counted (TRUE=1, FALSE=0) 
Text that cannot be interpreted as a number, typed directly into the list of arguments  #VALUE! error  #VALUE! error 
Logical values, within arrays or reference arguments  Ignored  ARE counted (TRUE=1, FALSE=0) 
Text (including empty text "", text representations of numbers, or other text), within arrays or reference arguments  Ignored  Counted as zero 
Empty cells  Ignored  Ignored 
See the page on Variance in Excel for a comparison of the different Excel variance functions.
The following spreadsheet shows the Excel Vara function used to calculate the sample variance of the set of values in cells A1A4 and in cells A1A6.
Formulas:
 Results:

Note that, in the spreadsheet above, the function in cell B2 includes the values in cells A5 and A6. In this case, the logical value TRUE in cell A5 is treated as the value 1 and the text in cell A6 is treated as the value 0. This is shown by the example in cell B3, in which cells A1A4 and the values 1 and 0 give the same result as the variance calculation for cells A1A6.
For further details and examples of the Excel Vara function, see the Microsoft Office website.
If you get an error from the Excel Vara Function, this is likely to be one of the following:
#DIV/0!    Occurs if fewer than 2 numeric values have been supplied to the function. 
#VALUE!    Occurs if any values that are supplied directly to the Vara function are text values that cannot be interpreted as numbers. 