Appropriateness of the standard mortality/incidence ratio in evaluation of completeness of population-based cancer registry data.

BACKGROUND The magnitude of differences in mortality incidence (M:I) ratios derived from the national mortality source and those derived from cancer registry (CR) databases may be used to determine associated factors. METHODS All information on cancer incidence cases and mortality cases from January 1, 2003 to December 31, 2007 were retrieved from 5 population-based cancer registries in four regions of Thailand. Two sources of mortality were used: death cases within the cancer registries and mortality statistics obtained from the Ministry of Public Health (MOPH). Plots of percentage M:I ratios from cancer registry databases and from national mortality sources against 1 minus 5 years relative survival (1-5yrRS) were used to visualize the correlation between the two mortality sources. A Poisson regression model was used to determine the influence of cancer sites and registries on the M:I ratio/[1-5yrRS]. RESULTS There was high variability between the standard M:I ratio derived from national mortality compared with 1-5 year RS. The factors affecting M:I ratios are sources of mortality data and misclassification of topographic site as the cause of death. CONCLUSIONS Use of the M:I ratio is not recommended to evaluate completeness of cancer registry data when the quality of mortality data is poor.