Completeness of Cancer Registration in Denmark 1943–1966 and Efficacy of Record Linkage Procedures

Abstract

The completeness of registration in the national, population based cancer registry in Denmark was evaluated for the first 23 years (1943-1966) of operation. The registry was linked to a complementary data file on 5674 Danish invasive cervical cancer patients enrolled in an international, clinical follow-up study on the basis of identifying information including name, month and year of birth and date of cervical cancer diagnosis. The cancer register had a deficit of 2.2% (95% confidence interval, 1.8-2.6) cervical cancer patients; this figure is low compared to those of other cancer registers. Some 80% of the identified cases were retrieved by computerized matching alone, and an additional 15% were identified by combining computerized and visual matching procedures. Scrutiny of non-retrieved case records revealed that major errors in the identifiers of the cohort used for linkage were responsible for inability to identify an additional 1.7%. The presents study underlines the importance of meticulously recorded, high quality key identifiers in registers, and linkage of cohorts to establish the presence or absence of disease.