Oral contraceptives and rheumatoid arthritis. Bias in observational studies of cause-effect relationships.
Spector
T D
TD
Silman
A J
AJ
D001172:Arthritis, Rheumatoid / Q000139:chemically induced*; D003276:Contraceptives, Oral / Q000009:adverse effects*; D004812:Epidemiologic Methods; D005260:Female; D006801:Humans
D003276:Contraceptives, Oral