Statistical methods
SECONDARY
Data analyses will be specified a priori in a statistical analysis plan, and analyses will be undertaken by the trial statistician using SAS version 9.4 (SAS Institute, USA). The binary outcomes will be analysed using a Linear Mixed Model with a logit link, with practice fitted as a random effect. Non-inferiority for the primary outcome will be evaluated by observing whether the lower bound of the two-sided 95% confidence intervals for the difference in screening coverage between the two groups is above the non-inferiority limit of -10. If non-inferiority is evident, assessment as to whether the implementation has effectiveness superior to that of the comparison group will be carried out using the same approach but comparing to a zero difference. The primary analyses will be carried out on an intention-to-treat basis. Per-protocol sensitivity analyses will also be conducted excluding participants who had major protocol violations. To account for any potential imbalance in underlying risk factors for screening uptake, sensitivity analyses will adjust for age, ethnicity, deprivation index, screening history and primary care practice. Analyses for the secondary outcomes will be conducted by age, ethnicity and screening status.