An environmental psychologist wanted to investigate whether a new eco-driving dashboard assistant was effective in reducing the number of hard-braking events for urban delivery drivers. Twenty delivery drivers completed a trial using the assistant. The researcher recorded the number of hard-braking events each driver experienced in the week following the installation of the assistant and compared it to the week prior to its installation.
Drivers who had fewer hard-braking events in the week following the installation than in the week prior were classified as 'Reduction' (+). Drivers who had more hard-braking events were classified as 'Increase' (-). Drivers who had the exact same number of hard-braking events were classified as 'No Change' (0).
Table 1
| Driver | Reduction (+) | Increase (-) | No Change (0) |
|---|---|---|---|
| 1 | + | ||
| 2 | 0 | ||
| 3 | + | ||
| 4 | - | ||
| 5 | + | ||
| 6 | + | ||
| 7 | - | ||
| 8 | + | ||
| 9 | 0 | ||
| 10 | + | ||
| 11 | + | ||
| 12 | - | ||
| 13 | + | ||
| 14 | + | ||
| 15 | 0 | ||
| 16 | + | ||
| 17 | + | ||
| 18 | - | ||
| 19 | + | ||
| 20 | + |
Calculate the sign test value of s s\,s for the data in Table 1. Explain how you reached 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.