population mean of a sample average
Sample Mean. The sample mean is the average of all the items in a sample (a group of observations). The following is the formula for the sample mean x of a set {x1, x2, ..., xn} of n observations from a given distribution: The population mean is the average of all the items in a population. Because a population is usually very large or unknown, the population mean is usually an unknown constant. An estimate of the population mean is the sample mean.