Measures

For measuring work engagement, we took the six items from the Utrecht Work Engagement scale specifically referring to vitality and dedication (Schaufeli et al., 2006), since this indicates autonomous motivation at work. A sample item referring to vitality at work is ‘At my work, I feel bursting with energy’. A sample item for dedication was ‘I am enthusiastic about my job’. Participants responded on a 7‐point response scale ranging from never (1) to always (7). Cronbach’s alpha’s were stable over time (T1 = .91; T2 = .94; T3 = .93).

General performance was measured with the single item indicator for general performance (Kessler et al., 2003) in which respondents are asked to rate their overall work performance during the last 4 weeks on a scale ranging from 0 to 10.

General health was measured with a single item ‘How would you rate your general health at this moment’ (Hooftman et al., 2017). Respondents answer on a 6‐point Likert scale ranging from very bad to very well.

For measuring self‐leadership strategies, eight subscales from the Revised Self‐leadership questionnaire (Houghton & Neck, 2002) were selected: self‐observation (four items, e.g., ‘I usually am aware of how well I’m doing as I perform an activity’), self‐goal setting (five items, e.g., ‘I establish specific goals for my own performance’), self‐cueing (two items, e.g., ‘I use written notes to remind myself of what I need to accomplish’), self‐reward (three items, e.g., ‘When I do an assignment especially well, I like to treat myself to some thing or activity I especially enjoy’), self‐punishment (four items, e.g., ‘I tend to get down on myself in my mind when I have performed poorly’), evaluation thoughts and assumptions (four items, e.g., ‘I think about my own beliefs and assumptions whenever I encounter a difficult situation’), self‐talk (3 items, e.g., ‘Sometimes I find I’m talking to myself (out loud or in my head) to help me deal with difficult problems I face’), and natural rewards (five items, e.g., ‘I seek out activities in my work that I enjoy doing’ and ‘I focus my thinking on the pleasant rather than the unpleasant aspects of my job activities’). Furthermore, we used the scale for self‐leadership behaviour (Yun, Cox, & Sims, 2006; six items, e.g., ‘I solve problems when they pop up without always getting my supervisor’s stamp of approval’). Cronbach’s alpha’s were stable over time (T1 = .81; T2 = .87; T3 = .88).

We controlled for organization (by creating four dummy‐variables), age and educational level, since these variables were related to the dropout within the experiment group throughout the intervention. We also controlled for job autonomy at T1, since job autonomy is seen as an important resource for work engagement, health, and performance of health care workers (Keyko, Cummings, Yonge, & Wong, 2016), while it is also an antecedent for self‐leadership (Stewart et al., 2011). Job autonomy was measured with the 9‐item job autonomy scale by Morgeson and Humphrey (2006). Employees responded on a 5‐point response scale ranging from strongly disagree (1) to strongly agree (5), and the scale showed sufficient reliability (α = .91).