Quality of case ascertainment in cancer registries: a proposal for a virtual three-source capture-recapture technique.

BACKGROUND The ability and behaviour of the capture-recapture method using a virtual three-source model for evaluation of the level of completeness of case ascertainment requires exploration. METHODS Cancer cases obtained from 9 population-based cancer registries in Thailand during 2003 to 2007 were applied for capture-recapture using a model based on clinical, pathological and mortality data. These three virtual sources were derived from three actual items common to all cancer registries: the basis of diagnosis, ICD-O morphology code, and last known patient status. Poisson regression models were fit to the data to estimate parameters which were then transformed into demographic values. A linear model was used to determine the predictors and estimated percentage of completeness (EPC) in case ascertainment among the cancer registries. RESULTS The EPC was greater than 97% in 5 and less than 90% in 4 registries. The worst had an EPC of 70%. The percentage death certificate only (%DCO) and the interaction between %DCO and morphological verification (MV) were significantly associated with EPC. Other factors intrinsic to registries also exerted influence on the EPC. CONCLUSIONS In addition to other standard indicators to monitor completeness of cancer registries, the present virtual three-source capture-recapture model can be routinely used to estimate the level of completeness of case ascertainment in cancer registries.