mean: the middle of a distribution; an estimate of the average score.

The mean of a group of scores (for example the mean height of all males on the local basketball team) is called a sample mean. The symbol for a sample mean is ("x-bar").

The mean for all values of a number (for example, the average height of all adult males everywhere in the world) is called the population mean. The symbol for population mean is (the greek letter "mu").

In most situations, the population mean can not be known directly- it has to be estimated with a sample mean, using a small sam