Validity and completeness of registration of surgically treated malignant gynaecological diseases in the Danish National Hospital Registry.

BACKGROUND The increasing tendency to acquire data by linkage to registries not designed for research has introduced a problem into epidemiological research. The data is often crude or possibly incomplete and, in some cases, it has been proposed to use these registries in the routine acquisition of data for existing epidemiological research registries. This study estimates the validity and completeness of the registration of surgically treated malignant gynaecological diseases in the Danish National Hospital Registry 1977-88. METHODS Completeness was estimated by the method of independent case ascertainment, by comparison with the registration of surgically treated gynaecological cancer cases registered in the Danish Cancer Registry. The validity of the diagnoses was analysed by comparison with the recoding of discharge summaries describing the admission of a 5% random sample. RESULTS The completeness of registration was 87% overall. Ovarian cancer, cervical cancer and cancer of the uterus were registered with a positive predictive value (PPV) of 89-90%. DISCUSSION The results of the study emphasise the need to consider the validation of Danish Hospital Registry data before linkage and analysis. In epidemiological cancer research the Danish Cancer Registry is the better alternative when information on malignant tumours is needed.