Average

In mathematics, there are numerous methods for calculating the average or central tendency of a list of n numbers. The most common method, and the one generally referred to simply as the average, is the arithmetic mean. Please see the table of mathematical symbols for explanations of the symbols used.

Arithmetic mean

The arithmetic mean is the standard "average", often simply called the "mean". It is used for many purposes and may be abused by using it to describe skewed distributions, with highly misleading results.

Related Topics:
Arithmetic mean - Mean - Skewed distribution

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A classic example is average income. The arithmetic mean may be used to imply that most people's incomes are higher than is in fact the case, or to protest that most people earn less than average. When presented with an "average" one may be led to believe that most people's incomes are near this number. This "average" (arithmetic mean) income is higher than most people's incomes, because high income outliers skew the result higher (in contrast, the median income "resists" such skew). However, this "average" says nothing about the number of people near the median income (nor does it say anything about the modal income that most people are near). Nevertheless, because one might carelessly relate "average" and "most people" one might incorrectly assume that most people's incomes would be higher (nearer this inflated "average") than they are. Consider the scores {1, 2, 2, 2, 3, 9}. The arithmetic mean is 3.17, but five out of six scores are below this!

Related Topics:
Average income - Outliers - Median

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In general, given n numbers, x_1, x_2, dots, x_n, their arithmetic mean is computed by the formula

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: ar{x} = {1 over n} sum_{i=1}^n{x_i}.

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