An educational psychologist investigated whether there is an association between secondary school students attending a voluntary early-morning mathematics study group (Yes/No) and achieving an A/A* grade in their end-of-year examination (Yes/No). They conducted a Chi-square test of association on the collected data. Part of the calculation table is shown below.
| Cell | Observed frequency (O) | Expected frequency (E) | O – E | (O – E)2^22 | (O – E)2^22 / E |
|---|---|---|---|---|---|
| A | 15 | 25.00 | –10.00 | 100.00 | 4.00 |
| B | 60 | 50.00 | 10.00 | 100.00 | 2.00 |
| C | 20 | 10.00 | 10.00 | 100.00 | 10.00 |
| D | 10 |
Formula for χ2\chi^2χ2:
χ2=∑(O−E)2E \chi^2 = \sum \frac{(O - E)^2}{E} χ2=∑E(O−E)2Calculate the overall value of Chi-square (χ2\chi^2χ2). Show your workings.
513 exam-style questions on OCR A Level Psychology Data recording, analysis and presentation. Each one has a worked solution and a mark scheme showing where the marks go.