5. LIMITATIONS
This study has several limitations. First, studies using administrative databases might be susceptible to errors arising from coding inaccuracies. To minimize this problem, we applied the definition validated in previous studies that used the Korean NHIS sample cohort.1, 2, 12, 24, 25Second, we were unable to define the type (paroxysmal vs. persistent) of AF. AF can occur without symptoms, and although numerous electrocardiography measurements were performed at the study center, some participants with asymptomatic AF might have been missed. Third, despite the adjustment for differences in baseline characteristics, residual unidentified confounders may remain.