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Business statistics

Function details

Note: The functions do not require the data given to them to be sorted. However, for reading convenience, most of the examples show sorted sequences.statistics.mean(data)

Return the sample arithmetic mean of data which can be a sequence or iterator.

The arithmetic mean is the sum of the data divided by the number of data points. It is commonly called “the average”, although it is only one of many different mathematical averages. It is a measure of the central location of the data.

If data is empty, StatisticsError will be raised.

Some examples of use:

>>> mean([1, 2, 3, 4, 4])
>>> mean([-1.0, 2.5, 3.25, 5.75])

>>> from fractions import Fraction as F
>>> mean([F(3, 7), F(1, 21), F(5, 3), F(1, 3)])
Fraction(13, 21)

>>> from decimal import Decimal as D
>>> mean([D("0.5"), D("0.75"), D("0.625"), D("0.375")])


The mean is strongly affected by outliers and is not a robust estimator for central location: the mean is not necessarily a typical example of the data points. For more robust, although less efficient, measures of central location, see median() and mode(). (In this case, “efficient” refers to statistical efficiency rather than computational efficiency.)

The sample mean gives an unbiased estimate of the true population mean, which means that, taken on average over all the possible samples, mean(sample) converges on the true mean of the entire population. If data represents the entire population rather than a sample, then mean(data) is equivalent to calculating the true population mean μ.