Faecal occult blood screening for colorectal cancer at Nottingham: details of the verification process

Cause specific mortality statistics derived from death certificates are highly dependent upon the accuracy of certification by the attending physician. In the Nottingham colorectal cancer screening trial, there were 12 624 deaths among the screening group and 12 515 among the control group during the period under consideration. There was no significant difference in all cause mortality rate (excluding deaths due to colorectal cancer) between the two study groups (rate ratio = 1.01, 95% confidence interval = 0.99 to 1.03). Disease specific mortality rates did not differ significantly between the two groups either. Overall, the agreement between verified and certified cause of death was 86%. Using the certified cause of death would have resulted in an underestimation bias of 6.27% for colorectal cancer deaths.