Source from which control participants reported they heard about the study and cost of recruitment per participant from each source
| Recruitment source | n | % | Cost per participant (GBP) |
| From a patient | 4 | 0.9 | 0.00 |
| HSR email | 4 | 0.9 | 0.00 |
| 2 | 0.5 | 0.00 | |
| 249 | 58.3 | 15.00 | |
| 3 | 0.7 | 0.00 | |
| Press | 1 | 0.2 | 0.00 |
| Word of mouth | 23 | 5.4 | 0.00 |
| VOICE | 8 | 1.9 | 0.00 |
| Missing* | 133 | 31.1 | 5.00 |
| Total | 427 | 100.0 |
*Number of participants recruited prior to amendment to the research protocol in September 2020 that included a new item measuring the source of recruitment.