The importance of content and face validity in instrument development: lessons learnt from service users when developing the Recovering Quality of Life measure (ReQoL).

<bold>Purpose: </bold>Service user involvement in instrument development is increasingly recognised as important, but is often not done and seldom reported. This has adverse implications for the content validity of a measure. The aim of this paper is to identify the types of items that service users felt were important to be included or excluded from a new Recovering Quality of Life measure for people with mental health difficulties.<bold>Methods: </bold>Potential items were presented to service users in face-to-face structured individual interviews and focus groups. The items were primarily taken or adapted from current measures and covered themes identified from earlier qualitative work as being important to quality of life. Content and thematic analysis was undertaken to identify the types of items which were either important or unacceptable to service users.<bold>Results: </bold>We identified five key themes of the types of items that service users found acceptable or unacceptable; the items should be relevant and meaningful, unambiguous, easy to answer particularly when distressed, do not cause further upset, and be non-judgemental. Importantly, this was from the perspective of the service user.<bold>Conclusions: </bold>This research has underlined the importance of service users' views on the acceptability and validity of items for use in developing a new measure. Whether or not service users favoured an item was associated with their ability or intention to respond accurately and honestly to the item which will impact on the validity and sensitivity of the measure. [ABSTRACT FROM AUTHOR]