
A statistical measure of central tendency, often the sum of values divided by the count.The average, or arithmetic mean, is a measure of central tendency that summarizes a set of numbers by a single representative value. It is calculated by summing all values and dividing by the count. While simple, it is one of the most widely used statistical tools because it provides a quick sense of the 'typical' value in a dataset. However, it is sensitive to extreme values, which can skew the result away from the center of the bulk of the data.
The concept of the arithmetic mean dates back to ancient times; it was used by Babylonian and Greek astronomers to combine multiple measurements. The formal term 'average' entered English from Arabic maritime law, where it referred to a tax or loss-sharing arrangement.
To compute the average, you add up all the observations and then divide by the number of observations. For example, the average of 2, 4, and 6 is (2+4+6)/3 = 4. This operation gives equal weight to every data point, which is both its strength and its weakness: it uses all information but can be distorted by outliers. In scientific analysis, the average is often used alongside other statistics like the median or standard deviation to provide a fuller picture.
Used everywhere from calculating climate temperature trends to determining the average lifespan of a particle in physics experiments, and in everyday contexts like grade point averages.
In a famous example, the average number of legs per human is slightly less than two, because a small number of people have one leg or none—showing how averages can be misleading for skewed populations.
| a(n) | variable | Number of unlabeled objects — count |
| n | variable | Size parameter (e.g., number of elements) — count |
| π | variable | Permutation in symmetric group — permutation |
| fix(π) | variable | Number of fixed points of permutation π — count |
| ∑ | operator | Sum over all permutations — summation |
| 1/n! | operator | Average over the group — average |




