To understand to what extent our estimates are affected by the assumption that the infection dates have been accurately observed, we randomized the estimated infection dates by adding a Gaussian noise with zero mean and a standard deviation of 2 days. This is motivated by the substantial proportion in the observed standard deviation (73.5% less or equal than 2 days) of the distribution time from the estimated infection date to the report date of IPs. We then fitted the simplest model (conditioned on both first infection and 23 rd February) to 10 such randomised datasets. The average estimates across them are given in Table 3 . They lie well within the confidence intervals we predicted in Table 1 . The average cattle:sheep infectivity ratio is also very close to the values estimated using the original data.