Figure 1.

Flow chart of the World Trade Center Health Registry systemic autoimmune disease study population. Systemic autoimmune diseases (rheumatoid arthritis, Sjӧgren's syndrome, systemic lupus erythematosus, polymyositis/dermatomyositis, mixed connective tissue disease, and scleroderma) were diagnosed in 2002 or later. Cases had to either meet disease‐specific classification criteria, have been diagnosed by a board‐certified rheumatologist, or have been prescribed a medication commonly used to treat systemic autoimmune disease.