A marine biologist investigated whether there is an association between the presence of a specific parasite (Yes/No) and the reef location (Inshore/Offshore) in a sample of coral trout. 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 | 24 | 18.00 | 6.00 | 36.00 | 2.00 |
| B | 14 | 20.00 | –6.00 | 36.00 | 1.80 |
| C | 12 | 18.00 | –6.00 | 36.00 | 2.00 |
| D | 26 |
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.