A researcher investigated whether using a blue-light screen filter before bedtime improves sleep quality. A sample of 25 participants rated their sleep quality before the trial and after one week of using the filter. The researcher categorized the changes in sleep quality as shown in Table 1 below.
| Improved sleep | Deteriorated sleep | Unchanged sleep | |
|---|---|---|---|
| Number of participants | 18 | 5 | 2 |
Explain two reasons why it was appropriate to use the sign test in this study. Refer to the details of the study in your answer.
121 exam-style questions on AQA A Level Psychology Inferential testing (A-level only). Each one has a worked solution and a mark scheme showing where the marks go.