Table 3 Summary of key contributions of expert service users at different stages, challenges and extra resource implications

1. Theme and item generation

Ensured that themes were relevant and that no themes were missing

Ensured that items generated were meaningful

Time for PI to prepare for (1 day) and attend 2 face-to-face meetings (2 days^a).

2. Face and content validity

Co-produced the topic guide

A service user researcher was involved in the interviewing and data analysis

The data analysis was reviewed by expert service users to help to reduce the number of items, ensuring the face and content validity of the measures

At the end of this stage, we were confident that no important item was missing and that items were appropriate

At the meeting to reduce the number of items (by about 40), expert service users added 58 extra items

Disagreement on certain items

Time for PI to prepare for (half day) and attend 2 face-to-face meetings (2 days ^a)

Time for researcher to prepare materials for Expert Service Users Group Meeting (2 days), attend the meeting (1.5 days), write up the feedback of the meeting (2 days)

Added 3 more weeks to the timeline to schedule 2 more core team meetings to reduce the number of items

3. Quantitative studies

Helped in making the final item selection

Ensured that the measures had face validity

Conveying psychometrics results to the expert service user group

Disagreements on certain items

Trade-off between psychometric properties and face validity

3 days for PI to prepare for meetings and 2 days to attend meetings

4. Implementation and dissemination

Contributed to making the research more accessible to others

Required support to work on papers and presentations

4 days of PI work to prepare and be involved in the filming.