In VDU work there are also other factors than keyboard and mouse usage acting as exposures. Work posture, for example, affects the overall work load. In the analysis of dose-response relationship, these additional factors should be taken into account as modifiers of exposure.
It is also apparent, that combining the data of computer usage into a few parameters per half a day does not give the best possible conception of a dose. In VDU work there are some faster and slower phases, pauses etc. during a workday. This variation of dose in time ( Mathiassen and Winkel 1991) should be considered thoroughly in the analysis. Our methods in collecting data will allow analysis of these time-related aspects of doses and responses.
Ketola, R., Häkkänen, M., Toivonen, R., Takala, E.-P.& Viikari-Juntura E. ( 1999). Ergonomics in VDU work: A randomized controlled trial. In Proc. 8th Int. Conference on Human-Computer-Interaction (HCI International '99, Munich, Germany, August 22-27, 1999)
Mathiassen, S. E. & Winkel, J. ( 1991). Quantifying variation in physical load using exposure-vs-time data. Ergonomics, 34 ( 12), 1455-1468.
Punnett, L. & Bergqvist, U. ( 1997). Visual display unit work and upper extremity musculoskeletal disorders, a review of epidemiological findings. Arbete och Hälsa 1997:16.