Standard deviation is calculated in Excel by using the formula SDEV(ARRAY), where ARRAY represents the range of numbers for which the standard deviation is being determined. This range is either a row or a column of cells on the Excel worksheet. Like all Excel formulas, SDEV is preceded by an equal sign when typed into a cell. The format must be "=SDEV(ARRAY)" for Excel to recognize it as a formula.
The formula SDEV is used to identify when a sample is being used. When the entire population is available, then the formula to use is SDEVP and the format is SDEVP(ARRAY). The range of numbers represented by ARRAY is represented in the formula in the format SDEVP(number1,number2, etc). The arguments in the formula can also be names, text or references that contain numbers. In order to include text representation of numbers, the formula SDEVA(ARRAY) is used.
Standard deviation is a measure of how far the values in a sample or population vary from the average value or mean. A small standard deviation means that the values are very close to the average value, whereas a large standard deviation indicates that the numbers are dispersed widely from the average. Standard deviation can therefore be used to calculate confidence in statistical conclusions. A small standard deviation implies greater confidence, while a greater standard deviation implies lesser confidence in statistical conclusions.