Data for: Prophylactic Effect of Sulfasalazine against Pneumocystis Pneumonia in Patients with Rheumatoid Arthritis: A Nested Case-Control Study

"MATCHED_STUDY" includes the data on PJP cases and their corresponding matched controls. "NONMATCHED_STUDY" includes the data on PJP cases and their corresponding non-matched controls (just matched on recorded years). The description of variables are explained in the files.