PAUL K. WILLIAMSON, M.D.
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To the editor: Steen and associates (1) have attempted to draw conclusions about the effect of D-penicillamine on the natural history of progressive systemic sclerosis with diffuse scleroderma.
In prospective studies, the random assignment of patients to treatment or control groups results in two similar samples from which conclusions can subsequently be drawn after therapeutic interventions. In retrospective studies, this assignment has already been made not randomly but on clinical grounds, and subtle group differences may occur. For example, in the study by Steen and associates (1), a patient may have developed mild proteinuria during the sixth month and D-penicillamine
WILLIAMSON PK. Penicillamine and Progressive Systemic Sclerosis. Ann Intern Med. ;98:675–676. doi: 10.7326/0003-4819-98-5-675_3
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Published: Ann Intern Med. 1983;98(5_Part_1):675-676.
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