Point and period prevalence of vibration-induced white finger (VWF) as a function of exposure time. The data sets are shown as asterisks and capped at the year 1970. The point prevalence model obtained from equation (4) up to the 4th-order with the respective parameter values from Table 1 with the time-dependent exposure factor of the respective period prevalence data set fitted by introducing is shown by the continuous line for: a) the 1958 data, b) the 1962 data and c) the 1966 data. The dash-dotted line shows the model fitted to the respective period prevalence data, i.e., equation (2) up to i = 4 with the values for a₁–a₄ from Table 1 without , to show its influence on the relation between prevalence and exposure time.