Our estimated average lead-time is based on incidence rates after 2 screening rounds (Norway) or 5 screening rounds or more (Sweden). We compare with the expected incidence rates when we calculate the average lead-time, and have adjusted for an underlying incidence increase by using regression analysis modelling the underlying incidence increase.

Because the observed average lead-time in the screening programme is smaller than in the randomized screening trials and that the rate of interval cancers is higher, it is likely that reduction in breast cancer mortality rates will be small than in the randomized screening trials (mortality reduction in the screening trials varies between 0 and 30%).