VDU-screen filters: remedy or the ubiquitous Hawthorne effect?

The claim that visual display units (VDU)-screen filters improve health by reducing exposure to electrical fields and/or improving screen legibility w as investigated by introducing VDU screen filters into an office environmen t. The study design was quasi-experimental, with the first part conducted a ccording to a simulated control group design with one intervention and one control group. In the second part, which served as a partly switched replic ation, the control group also received screen filters. The first group cont inued their use. The dependent measures were sick leave, productivity. subj ective symptoms, and musculoskeletal condition. Subjectively reported sympt om improvement was found in the group that received screen filters during t he initial part of the study, but that was followed by an aggravation of sy mptoms during the second part for the same group. No effect was observed in the control group in either part of the study. The discontinuity observed between the study parts indicates that factors other than VDU-screen filter use were responsible for the results. However, the results appear to be ex plained by subject reactivity, i.e. the Hawthorne effect. The results cauti on against premature conclusions drawn from short-term interventions and em phasise the need for a better understanding of the various psychological an d task-related factors that influence subjects. Relevance to industry Visual display units (VDU) are widely used in industry. Knowledge of potent ial VDU-related health hazards can improve workers health and performance. (C) 2001 Elsevier Science B.V. All rights reserved.