4 A psychologist investigated the scores of pairs of twins on an aptitude test. Seven pairs of twins were chosen randomly, and the scores are given in the following table.
| Elder twin | 65 | 37 | 60 | 79 | 39 | 40 | 88 |
| Younger twin | 58 | 39 | 61 | 62 | 50 | 26 | 84 |
- Carry out an appropriate Wilcoxon test at the \(10 \%\) significance level to investigate whether there is evidence of a difference in test scores between the elder and the younger of a pair of twins.
- Explain the advantage in this case of a Wilcoxon test over a sign test.