If you use Microsoft Excel on a regular basis, odds are you work with numbers. Put those numbers to work. Statistical analysis allows you to find patterns, trends and probabilities within your data. In this MS Excel tutorial from everyone's favorite Excel guru, YouTube's ExcelsFun, the 81st installment in his "Excel Statistics" series of free video lessons, you'll learn how to construct confidence intervals when the sigma (population standard deviation) is known. See how the CONFIDENCE and NORMSINV functions work.