# Chi squared test of independence

## Learning outcomes

On watching this video, students should be able to:

- Recall that a chi-squared test of independence can be used for two categorical variables and write down the null hypothesis for this test
- Explain the basic idea of a chi-squared test, namely that the test statistic is based on the observed minus expected frequencies in each cell, and that this follows a chi-squared distribution with (rows-1)*(columns-1) degrees of freedom under the null hypothesis, where rows and columns refer to the number of rows and columns in the contingency table.
- State that a chi-squared test only tests for independence and that the chi-squared distribution cannot be used to estimate a parameter or measure of association or effect. A chi-squared test is just a hypothesis test.