Point prevalence of vibration-induced white finger (VWF) as a function of exposure time. Here, only the higher prevalence data given in Bovenzi [31] for the stone and forestry workers are assumed to be known, shown by an asterisk and open circle, respectively, and the prevalence is interpolated from that value using linear interpolation (dashed lines) and polynomial interpolation (continuous lines). The second (lower) prevalence point is assumed to be unknown and is shown by a plus sign (stone workers) and a filled circle (forest workers). The prevalence model uses equation (7) that includes the calculated exposure factor by means of equation (6). A horizontal (dotted) line at 10% prevalence shows the target prevalence of some studies [6, 28].