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

- Dealing with the frequencies classified according to one set of categories
- Each item sampled contributes to only one frequency category (that is the categories are mutually exclusive)
- Looking for a difference between an observed frequency distribution of a single sample and an expected frequency distribution based on theoretical reckoning

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)