bb Ray 2011.

Methods	Case‐control study
Participants	Cases (n = 415): people with diagnosis of definite rheumatoid arthritis based on American College of Rheumatology criteria. Controls (n = 1245): matched for age and number of medical visits before index date.
Interventions	Exposure to influenza vaccine. Different times intervals before symptom onset were considered (90, 180, 365, and 730 days). Vaccine exposure status was determined from Kaiser Immunization Tracking System and supplemented by chart reviews. Risk of association was, moreover, also determined for tetanus and hepatitis B vaccines.
Outcomes
Notes	This study was funded by the Centers for Disease Control and Prevention Vaccine Safety Datalink Project.
Risk of bias
Bias	Authors' judgement	Support for judgement
CC ‐ case selection All outcomes	Low risk	Included as cases the incident cases from the cohort analysis and additional new onset cases identified from the study population whose symptoms began during 1996.
CC ‐ control selection All outcomes	Low risk	Same population
CC ‐ comparability All outcomes	Unclear risk	Poor matching
CC ‐ exposure All outcomes	Low risk	NCKPHP databases
Summary assessment	Unclear risk	Unclear