In the Results section, under the subheading, "Comparison of MTX + LEF with MTX/LEF, " the first sentence in the third paragraph should not include adjusted HRs (aHRs) as the values refer to crude incidence: "Considering the risk of laboratory abnormalities comparing MTX + LEF with the MTX or LEF group, there were numerically higher incidence of anemia (0.7, 95% CI 0.4-1.2 per 100 PY vs 0.4, 95% CI 0.2-0.6 per 100 PY, respectively), and elevation of hepatic transaminases (0.6, 95% CI 0.3-1.1 per 100 PY vs 0.3, 95% CI 0.1-0.5 per 100 PY, respectively) in the former group." In the Table 3 footnotes, biologic DMARDs/tofacitinib should not be included in the legend "b". The correct legend is, " b Adjusted for age, baseline DAS28, disease duration, sex, current smoking, seropositivity for rheumatoid factor or anti-CCP, history of malignancy, diabetes, hypertension, hypercholesterolemia, renal failure, ischemic cardiomyopathy, COPD, heart failure, use of sulfasalazine, antimalarials, corticosteroids, starting year, osteoporosis, and hepatitis B and C." The errors do not affect the results or conclusions of the study.