Does the source of death information affect cancer screening efficacy results? A study of the use of mortality review versus death certificates in four randomized trials

Background Often in randomized controlled trials of cancer screening, cause of death is determined by a mortality review committee. However, little is known regarding how findings from mortality review compare to those from death certificates alone. Purpose To examine the results of four different U.S. trials of cancer screening when death certificate data only were used, as compared to results using all available mortality review information. Methods Trials included were the Health Insurance Plan of New York breast screening trial (HIP), the Minnesota trial of fecal occult blood testing, and the Johns Hopkins and Mayo Lung Projects, which each examined chest x-ray and sputum cytology. The sensitivity, specificity, positive and negative predictive values, and Cohen's kappa for death certificates were calculated for all arms of all trials. Separate intention-to-screen analyses were conducted for each trial using cause of death information from either death certificates alone or full mortality review data. Results Generally there was excellent agreement between the death certificates and the mortality review committee as to the underlying cause of death (kappa > 0.85 in all cases); death certificate agreement was similar between arms in all trials. Modest changes in the screening effectiveness estimates were observed when mortality review information was utilized, ranging from a 9% decrease to a 2% increase in the calculated mortality rate ratios. However, in one instance (HIP) a statistically significant benefit of screening was observed when mortality review committee data were used (rate ratio (RR) 0.77, 95% confidence interval (CI) 0.62- 0.95) but not when death certificate data were used (RR 0.82, 95% CI 0.65-1.03). Limitations Although considered to be the gold standard, even carefully conducted mortality review may result in errors in cause of death assignment. Conclusions For each trial, results were similar regardless of the source of cause of death information. Clinical Trials 2010; 7: 69-77. http://ctj.sagepub.com.