Abstract
BACKGROUND: Interventions in occupational health often target worksites rather than individuals. The objective of this paper is to describe the (lack of) stability in units of analysis in occupational health and safety intervention projects directed toward worksites. METHODS: A case study approach is used to describe naturally occurring organizational changes in four, large, Nordic intervention projects that ran 3-5 years, covered 3-52 worksites, cost 0.25 mill-2.2 mill euro, and involved 3-7 researchers. RESULTS: In all four cases, high rates of closing, merging, moving, downsizing or restructuring was observed, and in all four cases at least one company/worksite experienced two or more re-organizations during the project period. If individual worksites remained, ownership or (for publicly owned) administrative or legal base often shifted. Forthcoming closure led employees and managers to seek employment at other worksites participating in the studies. Key employees involved in the intervention process often changed. CONCLUSION: Major changes were the rule rather than the exception. Frequent fundamental changes at worksites need to be taken into account when planning intervention studies and raises serious questions concerning design, analyses and interpretation of results. The frequent changes may also have deleterious implications for the potential effectiveness of many real life interventions directed toward worksites. We urge researchers and editors to prioritize this subject in order to improve the quality of future intervention research and preventive action.