How to Use the t Distribution in Python

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The t Distribution, also known as the Student’s t Distribution, is a type of probability distribution that is symmetric and bell-shaped, similar to the normal distribution, but has heavier tails. This distribution is often used when the sample size is small, and the population standard deviation is unknown.

In hypothesis testing, especially for small samples, it’s often used for constructing confidence intervals and performing t-tests. It is also useful in the analysis of regression data.

Python provides robust tools and libraries to work with the t distribution, offering functionalities for data generation, transformation, analysis, and visualization.

Using the t Distribution in Python

Python’s scipy library contains the scipy.stats module, which provides a set of functions and classes for working with the t distribution and many other statistical distributions.

Generating a t Distribution

Let’s look at an example of how to generate a random variable that follows a t distribution.

First, import the necessary libraries:

import numpy as np
from scipy.stats import t
import matplotlib.pyplot as plt

Now, we can generate a t distributed random variable. Let’s say we’re working with a sample size of 10 (which makes the degrees of freedom 9).

# Set the degrees of freedom
df = 9

# Generate the random variable
rv = t.rvs(df, size=1000)

print(rv[:5])  # print first five values

Here, rvs function generates random variates from the t distribution. df represents the degrees of freedom, usually equivalent to the sample size minus one. The size parameter specifies the number of random variates. If you print the first five variates, you’ll see that they are values drawn from a t distribution.

Plotting a t Distribution

A histogram is a great way to visualize a distribution of data. We can use it along with the probability density function (PDF) of the t distribution to visualize the generated data. Let’s do this:

# Plot the histogram of the random variables
plt.hist(rv, density=True, bins=30, alpha=0.5, label='Simulated data')

# Define the x range for the PDF
x = np.linspace(t.ppf(0.01, df), t.ppf(0.99, df), 100)

# Plot the PDF
plt.plot(x, t.pdf(x, df), 'r-', lw=5, alpha=0.7, label='t pdf')

# Add a legend

# Show the plot

This code will give you a histogram of the generated t distributed data along with the theoretical t probability density function. As the amount of data increases, the histogram should become more similar to the theoretical PDF.

t-test Using Scipy in Python

A common use case for the t-distribution is hypothesis testing – specifically, the t-test. A t-test compares the means of two groups and determines the significance of the difference. The scipy.stats module provides the ttest_ind function, which conducts an independent two-sample t-test. Let’s run a t-test on some sample data:

from scipy.stats import ttest_ind

# Generate two sets of data
data1 = t.rvs(df, size=100)
data2 = t.rvs(df, size=100)

# Perform the t-test
t_stat, p_val = ttest_ind(data1, data2)

print(f'T-statistic: {t_stat}')
print(f'p-value: {p_val}')

In this example, ttest_ind performs the t-test on two independent samples. The function returns the t-statistic and the p-value. If the p-value is small (typically, less than 0.05), we reject the null hypothesis that the means of the two groups are equal.


The t-distribution is a fundamental distribution in statistical analysis, especially when dealing with small sample sizes. Python provides powerful tools that allow us to work with the t-distribution effectively. Using the scipy library, we can generate t-distributed data, plot the distribution, and perform t-tests. As always, it is important to understand the statistical assumptions and implications when working with statistical distributions.

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