Measurements on any variable, even the same variable on the same subject, will always vary. The pattern of variation of a variable is called its distribution, which can be described both mathematically and graphically. In essence, the distribution records all possible numerical values of a variable and how often each value occurs (its frequency). The most famous example of a distribution is the bell-shaped curve. To see examples of several types of distributions, see the ``How are things distributed'' concept lab.