The statistical symbol x-bar represents a sample mean in contrast to the Greek symbol mu, which looks similar to a u and represents the population mean. To include the x-bar symbol in regular text, combine diacritical marks or use Alt-Codes for the quickest solution, but within equations, use accents to construct the symbol.
Alt-Codes offer the quickest method of entering the x-bar symbol, because you don't need to open additional dialogs, and the effect is identical to using the Symbols dialog to add the horizontal bar. Word 2013 contains two appropriate Alt codes: 0772 and the slightly longer bar 0773.
Type an x where you want the x-bar symbol to appear, and then hold down the Alt key.
Type 0772 or 0773 using your numeric keypad. When you release the Alt key, the bar appears above the x.
Using the Symbol Dialog
Type an x where you want the x-bar symbol to appear.
Click the Insert tab, select Symbol from the Symbols group and choose More Symbols.
Double-click the 0304 or 0305 character, listed under Combining Diacritical Marks. Adding these marks is identical to using the 0772 or 0773 Alt-Codes, respectively.
Using the Equation Editor
Click the Insert tab and select Equation from the Symbols group.
Select the Design tab, click the Accent drop-down menu from the Structures group and choose the Bar symbol.
Click the empty square with the bar on top and type an x. When you click outside the equation, the x-bar symbol displays normally.