NUMBAT OER - Open Educational Resources

When to use it:

You should use a two-way Chi-square test when:

  • Dealing with the frequencies classified accoring to two sets of categories in a contingency table.
  • Each item sampled contributes to only one cell in the contingency table.
  • Looking for a difference between an observed frequency distribution of a single sample and an expected frequency distribution based on no association between the two variables.

Do not use this test when:

  • Using descriptive statistics, percentages or anything other than frequencies.
  • Expected values include small values. As a rule of thumb: If any expected value is zero or more than one fifth of the expected values are less than five, the chi-square test becomes unreliable. (Note that's expected values: it does not matter what the observed values are)