The response rates for fixed, confirmable and open invitations were 75%(95% CI 71 to 79), 69%(95% CI 65 to 74) and 54%(95% CI 49 to 59) respectively. However slot coverage rates were lower for fixed appointments, 80%(95% CI 76 to 84, p< 0.0001), than for the other two methods of invitation: 95%(95% CI 92 to 97) for confirmable and 98%(95% CI 95 to 99) for open. The difference between the above results for the three methods of invitation were statistically significant, with the exception of:(a) response rate of fixed vs confirmable appointment (difference=6, 95% CI -1 to 12, p = 0.083); (b) Slot coverage rate of confirmable vs open appointment (difference=3, 95% CI -3 to 6, p=0.094).