Effect of a participatory ergonomics intervention on psychosocial factors at work in a randomised controlled trial

Objectives To study the effect of a participatory ergonomics intervention on psychosocial factors among kitchen workers. Design A cluster randomised controlled trial. Setting Four cities in Finland, 2002-2005. Participants 504 workers in 119 municipal kitchens. Intervention Kitchens were randomised to intervention (n = 59) and control (n = 60) groups. The intervention lasted 11-14 months and was based on the workers' active participation in work analysis, planning and implementing the ergonomic changes aimed at decreasing the physical and mental workload. Main outcome measures Mental stress, mental strenuousness of work, hurry, job satisfaction, job control, skill discretion, co-worker relationships and supervisor support. Data were collected by questionnaire at baseline, at the end of the intervention, and at a 12-month follow-up (PI12). Results At the end of the intervention, the OR of job dissatisfaction for the intervention group as compared with the control group was 3.0 (95% CI 1.1 to 8.5), of mental stress 2.3 (1.2 to 4.7) and of poor co-worker relationships 2.3 (1.0 to 5.2). At the PI12, the OR of job dissatisfaction was 3.0 (1.2 to 7.8). Analysis of the independent and joint effects of the intervention and unconnected organisational reforms showed that adverse changes were accentuated among those with exposure to both. Conclusions No favourable effects on psychosocial factors at work were found. The adverse changes were due to a joint effect of the intervention and the unconnected organisational reforms. The findings do not support the usefulness of this kind of intervention in changing unsatisfactory psychosocial working conditions.