In statistics, x bar is a symbol used to represent the sample mean, or average, of a set of values. The Latin small letter x is used to represent a variable in a set of sample data, and a horizontal bar over the letter indicates that it represents the average or mean of whatever the variable represents. To calculate the sample mean, all the data points in the sample are summed up and then divided by the number of data points. The formula for the sample mean is x̄ = (Σ xi) / n, where x̄ is the sample mean, Σ is summation notation meaning "add up," xi represents all the x-values, and n is the number of items in the sample. The sample mean is one of three measures of central tendency for data, the others being the median and mode.