ute on each type of variable. Statistics that simply involve counting of different values (such as the most common value, known as the <em>mode</em>), can be calculated on any of the variable types. Other statistics are based on ordering or ranking of values (such as the <em>median</em>, which is the middle value when all of the values are ordered by their magnitude), and these require that the value at least be on an ordinal scale. Finally, statistics that involve adding up values (such as the average, or 