In MS-Excel 2007, STDEV(number1, number 2, ... ) is a statistical function that

In MS-Excel 2007, the STDEV function is used to estimate the standard deviation based on a sample of a population. It is one of the most commonly used statistical functions for data analysis. Key characteristics include:

• Sample Basis: It assumes that its arguments are a sample of the population. If the data represents the entire population, the STDEVP function should be used.
• Exclusion: It ignores logical values (TRUE/FALSE) and text that appear in arrays or cell references.
• Calculation: It uses the "n-1" method (Bessel's correction) to calculate the square root of the variance.

If you need to include logical values and text in the calculation (treating TRUE as 1 and FALSE/text as 0), you would use the STDEVA function instead.