Discussion
This paper aimed to operationalise an approach to intervention acceptability that: (a) ensured that a large representative sample of people with lived experience is involved in the process of improving intervention acceptability; and (b) adopted a theory-driven, experimental approach to evaluating whether refining an intervention based on participant feedback increases acceptability. To our knowledge, this is the first study to apply the TFA to develop an experimental approach to assess whether incorporating participant feedback brings about improvements in intervention acceptability.Although the number of participants exceeded the required numbers based on prior power calculations, there were no statistically significant differences in acceptability ratings between the control group (the original intervention) and the intervention group (a modified version of the volitional help sheet based on participant feedback) at six-month follow-up. Consequently, more changes may be required to the modified intervention to further increase acceptability. Future research should therefore aim to build on our findings and examine how making further adaptations may affect perceptions of acceptability, with a focus on two specific domains: 