Vibration-induced white finger (VWF) point prevalence data as a function of exposure time from Bovenzi [31] for stone workers shown as asterisks. In (a) and (b), the fit to all known data points is shown by the continuous line. In (a), the exposure factor is a fixed value calculated using equation (6) as included in equation (7) that is used for the prevalence model, and in (b) the exposure factor is a time-independent additional fit parameter and the prevalence model uses equation (3) with the 4th-order parameters. is an adjustable fit parameter in both models. In (a), the model with the fit parameter set to zero (dashed line) shows the effect of when the same calculated exposure factor is used.