Modelling prevalence development in a population group exposed to vibration, and noise: Application to hand-transmitted vibration

An invertible, generalisable population model for the time course of the prevalence of a health effect resulting from habitual exposure to a physical agent, such as vibration, and noise, is proposed. The model includes a time-dependent factor representing the daily exposure, expfac(t), applied to a polynomial fit of prevalence-time data recorded in a population group and one additional numerical parameter, a'1, to adjust the model for exposure-specific conditions. A model is constructed for the prevalence of vibration-induced white finger (VWF) to confirm and validate its performance. A 4th-order polynomial fits representative data recorded in a population group from the commencement of exposure. Using the same polynomial coefficients and solely adjusting expfac(t) enables the model to fit period prevalence data for VWF from all available population groups as a function of time. Adjusting a'1 enables the model to predict the point prevalence. If expfac(t) is specified in terms of the daily 8-h, energy-equivalent, frequency-weighted triaxial acceleration, the prevalences observed in different populations groups can be interrelated and interpolated to a common value (e.g., 10%) by inverting the model. This will enable tolerable daily exposures suitable for occupational environments to be defined for hand-transmitted vibration.