2 Part of Helen’s psychology dissertation involved the reaction times to a certain stimulus. She measured the reaction times of 30 randomly selected students, in seconds correct to 2 decimal places. The results are shown in the following stem-and-leaf diagram.
| 14 | 1 | 2 | | | | | | | |
| 15 | 2 | 4 | | | | | | | |
| 16 | 0 | 3 | 6 | | | | | | |
| 17 | 1 | 5 | 7 | | | | | | |
| 18 | 3 | 4 | 5 | 7 | 9 | | | | |
| 19 | 2 | 4 | 6 | 7 | 8 | 9 | | | |
| 20 | 0 | 1 | 3 | 4 | 5 | 7 | 8 | 9 | |
| 21 | 7 | | | | | | | | |
Key: 18 | 3 means 1.83 seconds
Helen wishes to test whether the population median time exceeds 1.80 seconds.
- Give a reason why the Wilcoxon signed-rank test should not be used.
- Carry out a suitable non-parametric test at the \(5 \%\) significance level.