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How can I calculate the variance of a list in python?

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How can I calculate the variance of a list in python?

  1. How can I calculate the variance of a list in python?

    Well, there are two ways for defining the variance. You have the variance n that you use when you have a full set, and the variance n-1 that you use when you have a sample.

  2. calculate the variance of a list in python

    Well, there are two ways for defining the variance. You have the variance n that you use when you have a full set, and the variance n-1 that you use when you have a sample.

Method 1

Starting Python 3.4, the standard library comes with the variance function (sample variance or variance n-1) as part of the statistics module:

from statistics import variance
# data = [-14.82381293, -0.29423447, -13.56067979, -1.6288903, -0.31632439, 0.53459687, -1.34069996, -1.61042692, -4.03220519, -0.24332097]
variance(data)
# 32.024849178421285

The population variance (or variance n) can be obtained using the pvariance function:

from statistics import pvariance
# data = [-14.82381293, -0.29423447, -13.56067979, -1.6288903, -0.31632439, 0.53459687, -1.34069996, -1.61042692, -4.03220519, -0.24332097]
pvariance(data)
# 28.822364260579157

Also note that if you already know the mean of your list, the variance and pvariance functions take a second argument (respectively xbar and mu) in order to spare recomputing the mean of the sample (which is part of the variance computation).

Method 2

Well, there are two ways for defining the variance. You have the variance n that you use when you have a full set, and the variance n-1 that you use when you have a sample.

The difference between the 2 is whether the value m = sum(xi) / n is the real average or whether it is just an approximation of what the average should be.

Example1 : you want to know the average height of the students in a class and its variance : ok, the value m = sum(xi) / n is the real average, and the formulas given by Cleb are ok (variance n).

Example2 : you want to know the average hour at which a bus passes at the bus stop and its variance. You note the hour for a month, and get 30 values. Here the value m = sum(xi) / n is only an approximation of the real average, and that approximation will be more accurate with more values. In that case the best approximation for the actual variance is the variance n-1

varRes = sum([(xi - m)**2 for xi in results]) / (len(results) -1)

Ok, it has nothing to do with Python, but it does have an impact on statistical analysis, and the question is tagged statistics and variance

Note: ordinarily, statistical libraries like numpy use the variance n for what they call var or variance, and the variance n-1 for the function that gives the standard deviation.

Summery

It’s all About this issue. Hope all Methods helped you a lot. Comment below Your thoughts and your queries. Also, Comment below which Method worked for you? Thank You.

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