2.3 Definition of cases and selection of controls
Patients included those who experienced serious GI complications,
defined as hospitalizations or emergency department visits, with the
main diagnosis of GI bleeding or perforation. GI complications from the
upper GI tract, such as the stomach, to the lower GI tract, such as the
duodenum, were also included. The diagnostic codes for GI complications
according to the ICD-10 codes are summarized in Table S1. The index date
for cases was the date of diagnosis of serious GI complications. We
randomly selected 1:10 matched controls for NSAID use duration. We
assigned an index date to the controls equal to that of the
corresponding cases.