An example of record linkage methods to monitor mortality and cancer incidence

Linkage of New York State record systems was the key strategy in a restrospective cohort study with a 24-34 year followup interval. Parents of children with anencephaly or spina bifida and matched control parents were traced to determine the parents' cancer and death experience. Birth certificates for Upstate New York for 1945-55 were the source of the study groups. This report describes the methodology employed. The New York State Health Department's Cancer Registry and vital records, the State motor vehicle license files, and city and phone directories were searched for the most recent record indicating residence in Upstate New York, cancer incidence, or death.Among the parents of the 1,152 index children were 18,571 person-years of followup for mothers and 21,675 person-years for fathers. Among the 1,152 controls, there were 19,682 person-years of followup for mothers and 22,596 person-years for fathers. Although losses were larger than the optimal, a large proportion of the maximum possible person-years were obtained, regardless of the birth year of the index child. Patterns of loss to followup were similar for cases and controls.Record linkage techniques are especially applicable in followup studies if the risk factor is identifiiable from routinely collected information (for example, congenital neural tube defects listed on birth certificates) and the outcome is also identifiable from such records (for example, cancer registry certificate or death certificate). If the outcome is definitive, reported routinely and comprehensively, and stored on a machine-readable medium, use of a computerized record linkage design is very efficient. A major advantage of the design is that cases and controls are treated equally with respect to outcome ascertainment and followup, so that some potential biases are eliminated. Finally, the method is non-intrusive; the subjects are never contacted or interviewed. Strictly maintained confidentiality is, of course, required.