Mean rank of scores by number of previous experiences with nitrous oxide
| Phase | 1a | 1b | 2 | 3a | 3b | 4 | Total |
| 0 | 47.8 | 50.9 | 44.7 | 47.7 | 46.1 | 47.6 | 50.0 |
| 1–5 | 43.7 | 41.6 | 44.5 | 41.5 | 42.7 | 43.4 | 40.5 |
| 6–10 | 43.2 | 39.5 | 47.9 | 45.3 | 47.2 | 43.8 | 42.3 |
| p value | 0.652 | 0.136 | 0.777 | 0.627 | 0.603 | 0.695 | 0.288 |
p < 0.05.