BMC Public Health 2009, 9:140 http://www.biomedcentral.com/1471-2458/9/140 ranged from 0.79 to 0.95, which we considered as good internal reliability [46]. The construct and concurrent validity of the VBBA core questionnaire are satisfactory [46]. Self-efficacy for return to work We measured 'self-efficacy for return to work' by using a recently developed questionnaire. Jager [47] found, in a pilot study of workers on sick leave due to CMDs, a satis- factory construct validity and good reliability: the Cron- bach's alpha was 0.94, and test-retest reliability 0.75. Coping behaviour We measured coping behaviour by using an adapted ver- sion of the shortened 19-item version of the original 30- item Utrecht Coping List (UCL) [48,49]. This self-report questionnaire was designed to measure the coping behav- iour people use in stressful situations, life events, or daily hassles. We adapted the questionnaire so that all the items were concerned with problems at work. Each item was rated on a 4-point Likert scale ranging from 1 (never) to 4 (very often). The UCL includes 5 dimensions: (1) active problem-focusing (5 items), (2) seeking social support (5 items), (3) palliative reaction pattern (4 items), (4) avoid- ance behaviour (3 items), and (5) expression of emotions (2 items). Avoidance behaviour related to work To explore the concept of avoidance behaviour related to the return to work, we used two questions: Do you avoid emotional or stress-evoking work situations? Is your pro- ductivity negatively affected by this? Each question was scored on a 4-point Likert scale ranging from 1 (seldom or never) to 4 (very often). Patient satisfaction with counselling of OP We measured patient satisfaction with the counselling of the occupational physician by using the Patient Satisfac- tion with Occupational Health Services Questionnaire (PSOHQ) [50]. The questionnaire consists of 20 items and 4 subscales concerning 'being taken seriously as a patient', 'trust and confidentiality', 'expectations', and 'attitude towards occupational health services', respec- tively. The scales showed sufficient reliability [50]. Work adaptations We measured work adaptations by using two questions: (1) have work adaptations been made during the last three months (yes/no)? and (2) if yes, specify these work adaptations. Process measures Compliance of intervention We measured the compliance of the counselling process of OPs and their patients with the RTW-E programme by scoring the presence and quality of filled-in homework assignment forms. The presence of filled-in forms A (Task Inventory) to F (Evaluation of Work Tasks and Practice Situations) was scored by yes or no. The quality of the filled-in forms was classified by two researchers (EN and KN) independently. The quality of each form was rated on a 3-point Likert scale: 0 = not in accordance with the pur- pose of the form, 1 = partly in accordance with the pur- pose of the form, and 2 = in accordance with the purpose of the form. The total quality score of compliance was classified for each patient as low (< 3), moderate (3–6), or high (> 6). Communication employee-supervisor We measured communication between the employee and supervisor by using a two-item questionnaire, derived from a standardized telephone interview concerning supervisor behaviour related to return to work [51]. Economic evaluation measures In order to make a cost-effectiveness analysis, we calcu- lated the effectiveness of the primary outcomes, the costs, and the incremental cost-effectiveness ratio (ICER) for each group. The total cost calculations were made from a societal perspective as recommended for the evaluation of health care programmes [33]. This means that costs were calculated independently of those who bear these costs and receive benefits. To calculate the total costs, we measured the costs of con- suming health care (six items) and the costs of production loss (seven items) by an adapted version of the Trimbos/ iMTA questionnaire for costs associated with psychiatric illness [52]. Furthermore, we measured the travelling dis- tance to visit the OP, to calculate out-of-pocket costs. Except for the duration of sick leave, the items originate from the TiC-P questionnaire, which in turn originates from the Short-Form Health and Labor Questionnaire (SF-HLQ). We calculated the costs of production loss for each group by multiplying respectively the mean duration of sick leave and the mean production loss without sick leave (three items) with the mean net income from paid work (one item). The reported net income will be vali- dated with national data of income related to age and gen- der. If these data can not be considered valid or the income data of too many patients are unknown, we will use national data of average production value per worker related to age and gender. To calculate the costs of production loss due to sick leave, we used the friction-costs method [33]. This method cal- culates the loss of production until the vacancy because of sick leave is resolved. To calculate the costs of production loss without sick leave, we averaged the costs calculated by the method of Osterhaus and the costs calculated by the HLQ method, as Page 8 of 11 (page number not for citation purposes)