A test for whether observed frequencies differ from what a model predicts, and for whether two categorical variables are related.
Syllabus points covered
- Calculate expected frequencies for a goodness-of-fit test
- Carry out a goodness-of-fit test for given distributions
- Carry out a test for independence in a contingency table
- Determine the correct number of degrees of freedom and combine classes where expected frequencies are small
Common mistakes
- Not combining classes where the expected frequency falls below 5.
- Using the wrong degrees of freedom, particularly after estimating a parameter from the data.
- Calculating the test statistic with observed and expected values interchanged.
- Concluding 'the variables are independent' rather than 'there is insufficient evidence of association'.
Worksheets
Use these as soon as you've learned the topic and need to practise it. Start with the worksheet, check yourself against the answers, and only then look at the step-by-step solutions.
- Practice worksheetComing soon
- Worksheet answersComing soon
- Step-by-step solutionsComing soon
Topical past papers
Move on to these once you've worked through the worksheets and are ready for harder, exam-style questions. Real past-paper questions on this topic, with the official mark scheme and full worked solutions.
- Topical questions
- Mark scheme
- Step-by-step worked solutionsComing soon
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