ges outside of the range 12 – 54 years are automatically rejected. This should have been implemented in the PathLAN routines. A further alternative that would have helped would have been to report the age used in the calculation, rather than just the date of birth. This is of course easy to say with the benefit of the retrospectoscope – but should be a recommendation of any final report, to prevent others from having a similar problem.The most critical question is whether the software fix described above has truly repaired the PathLAN program and has returned the calculations to ‘normal’. I have yet to fully analyse the before & after data from PathLAN but I have carried out 2 exercises that make me 99% certain that all problems have been solved. Firstly, I calculated a prediction of the age-related underestimate of risk that would be expected if the only problem was the millennium bug described above (Figure 1)Figure 1: Predicted risk underestimate Then I took a selection of 30 patients with incorrect & correct risks representing a range of ages from 18 – 43 years, and derived the observed inaccuracy, and saw how this fits with prediction.Figure 2: Observed variation in Risk It is clear that the observed variations lie almost exactly on the predicted line. The slight variation is probably due to the date routine error. This means that for the randomly selected 30 patients, of the 7000 (approx) cases the agreement between predicted and observed is exact. It would be almost entirely unthinkable that this could have occurred by chance. Therefore, we can be effectively certain that all of the error was due to the Y2K bug described above. Once all of the data is available [data search currently being prepared], I will carry out a final test but this is really for completeness rather than to satisfy any lingering doubt.A Final test based on 6240 results and using the same graphical technique as figure 11 is show...
