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

Hello Guys, How are you all? Hope You all Are Fine. Today We Are Going To learn about How can I calculate the variance of a list in python in Python. So Here I am Explain to you all the possible Methods here.

## 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.