Materials and Methods
The single-payer compulsory National Health Insurance (NHI) program was initiated in Taiwan in 1995. The program provides universal coverage to most residents in Taiwan. The NHI Research Database (NHIRD) provided data about complete outpatient visits, hospital admissions, prescriptions, catastrophic illness information, and vital status of 99% of Taiwan’s 23 million people. The bureau of the NHI released the NHIRD for research purposes. In this study, we adopted the data obtained through the Longitudinal Health Insurance Database 2005 (LHID 2005) from the NHIRD. This LHID 2005 database included registration and medical claims for 1,000,000 randomly sampled patients from the total number of NHRI enrollees. The LHID2005 data set allows researchers to follow up on all the medical services utilized by these 1,000,000 individuals since the initiation of the NHI in 1995. To protect individual privacy, the original identification numbers of the beneficiaries’ data were encrypted for privacy. Encryption procedures were consistent with other datasets and ensured that all claims data could be linked in order to obtain additional medically relevant data. All data that could be used to identify patients or care providers, including the names of medical institutions and physicians, were encrypted. Our study protocol was approved by the institute review board of Chang Gung Memorial Hospital, Kaohsiung, Taiwan without the need of any informed consent.