Predicted time for BVDV herd prevalence to drop below 2% for three scenarios. (a) no movement of PI's (b) no movement of PIs via market. Times greater than 30 years are grouped in a single bar of the histogram. (c) restrictions from farms with the higher numbers of departure moves. The x-axis corresponds to the proportion of farms, n, ranked according to the number of departure moves, upon which movement restrictions are placed. The solid line represents the mean time with the upper and lower lines representing the first and third quartile respectively. All simulations are run using a closed network i.e. assuming a complete ban on movement of PIs into the network.