2.1 Study design
We conducted a population-based nested case-control study using the claims data of the Taiwan National Health Insurance program. Taiwan has implemented a mandatory health insurance program providing comprehensive medical care coverage to more than 99.9% of the 23 million residents[21].
We used the longitudinal dataset containing claims data for 1 million individuals randomly selected from people insured by the National Health Insurance program in 1996–2000. For each individual in the dataset, longitudinal medical records from 1996 to 2013 can be obtained by data linkage between inpatient files, outpatient files, prescription drugs, and registry for beneficiaries using an encrypted, unique personal identification number. This study was approved by the Institutional Review Board at the China Medical University Hospital.