Chi-Square Test for Goodness-of-Fit Explained: Step-by-Step Tutorial

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Blessing Ngoduru
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Welcome to our comprehensive tutorial on the Chi-Square Test for Goodness-of-Fit! In this video, we will dive deep into understanding this fundamental statistical test, which helps determine how well observed data matches expected data. By the end of this video, you’ll have a solid understanding of the Chi-Square Test for Goodness-of-Fit and how to apply it to your own data

Video Outline:
- Introduction to the Chi-Square Test for Goodness-of-Fit
- What is a Chi-Square Test?
- Understanding Observed vs. Expected Frequencies
- Example Problem and Solution
- Calculating the Chi-Square Statistic
- Determining Degrees of Freedom
- Finding the P-Value  
- Interpreting the Results
- Conclusion and Summary

Goodness-of-fit testing assess whether observed frequencies or data follows a specific probability distribution or model. That's it focuses on the fit of observed data to an expected distribution. Chi-square goodness-of-fit involves one categorical variable with multiple levels.

Example: Testing if observed data matches the expected frequencies of categories in a single population.

The statistical test used is the Chi-square goodness-of-fit test.

Video demonstrated "How to state the

Null and Alternative Hypothesis for a Chi-square Goodness-of-fit test.

For Chi-square Goodness-of-fit test, the Null hypothesis typically states that "there is no significant difference between the observed and expected frequencies in the population or group for the categorical variable under study. That's, observed frequencies matches the expected frequencies. The alternative hypothesis would then assert that there is no significant difference between the observed frequencies and expected frequencies.

Here is how you can formerly state them;

Null hypothesis: There is no significant difference between the observed frequencies and expected frequencies in the population for the categorical variable under study. Alternative hypothesis: There is a significant difference between the observed frequencies and expected frequencies in the population for the categorical variable under study.


Video shows "How to identify the procedure and check the conditions for using a Chi-square Goodness-of-fit test".


The following steps can help to identify when to use a Chi-square Goodness-of-fit test and ensure that the necessary conditions are met for valid results:

Identify the procedure:

A Chi-square Goodness-of-fit test is used to determine whether the observed distribution of a categorical variable differs from a theoretical or expected distribution.

A Chi-square Goodness-of-fit test is commonly used when you have one categorical variable with multiple levels (categories), and you want to compare the observed frequencies in each category with the expected frequencies.

Check the conditions:

Independence: The observations must be independent. Each observation should belong to only one category, and the categories should be mutually exclusive.

Sample Size: Each expected frequency should be at least five (5). If any expected frequency is too low (less than 5), you may consider combining categories to meet the assumption of expected frequencies greater than 5.


Video shows how to calculate Chi-square test Statistic and compare it to the critical value from the Chi-square distribution table with appropriate degrees of freedom.

Video also Interpreted the P-value and draw conclusion. If Test Statistic is less than the critical value, you can accept Null and conclude that there is no evidence of significant difference between the observed frequencies and expected frequencies.

Whether you’re a statistics student, researcher, or data analyst, this tutorial will help you grasp the essential concepts and apply the Chi-square Test for Independence confidently in your projects.

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