Background
Employee engagement is a fundamental component of quality healthcare. In order to provide empirical data of engagement in NHS Scotland an Employee Engagement Index was co-constructed with staff. `iMatter¿ consists of 25 Likert questions developed iteratively from the literature and a series of validation events with NHS Scotland staff. The aim of this study was to test the face, content and construct validity of iMatter.

Methods
Cross sectional survey of NHS Scotland staff. In January 2013 iMatter was sent to 2300 staff across all disciplines in NHS Scotland. 1280 staff completed it. Demographic data were collected. Internal consistency of the scale was calculated. Construct validity consisted of concurrent application of factor analysis and Rasch analysis. Face and content validity were checked using 3 focus groups.

Results
The sample was representative of the NHSScotland population. iMatter showed very strong reliability (??=?0.958). Factor analysis revealed a four-factor structure consistent with the following interpretation:

1. My experience as an individual

2. My experience with my direct line manager

3. My experience with my team

4. My experience with my organisation

Each subscale also showed high level of internal consistency within all disciplines. Rasch analysis confirmed the majority of items fit with the latent trait of staff engagement with infit statistics between 0.7 and 1.3; and showed a good spread of item difficulty covering person ability. Focus groups found the questionnaire valid it terms of brevity, relevance and clarity.

Conclusions
iMatter showed evidence of high reliability and validity. It is a popular measure of staff engagement in NHS Scotland. Implications for practice focus on the importance of coproduction in psychometric development.