Table 1

A comparison of the two case-referent studies included in the pooled analysis

Study of incident cases of RAStudy of prevalent cases of RA
*American Rheumatism Association (ARA) 1987 Revised Criteria for Rheumatoid Arthritis.22
†Morning stiffness >60 minutes and symmetrical arthritis and arthritis of small joints.
‡Cases and referents in the study using prevalent cases were recruited from the catchment area of the University Hospital in Linköping, situated in southeastern Sweden. Cases and referents in the study using incident cases were recruited from this area as well as from the catchment areas of nine other rheumatology units located in Southeastern Sweden.
§Age when responding to the postal questionnaire.
Exposure assessmentQuestionnaire basedQuestionnaire based
Occupational historyLifelongLifelong
Inclusion criteria
    ARA criteria* (n)⩾4 or 3 specific†⩾4
    Age at diagnosis, range (years)16–7525–75
    Year of diagnosis, range1996–981980–95
    ResidencySoutheastern Sweden‡Southeastern Sweden‡
Origin of casesHospital basedHospital based
No. included (n)298422
Age at diagnosis, mean (years)5554
Age at participation§, mean (years)5562
Inclusion criteria
    Age at enrolment, range (years)16–7525–75
    Year of enrolment, range1996–19981980–1995
    ResidencySoutheastern Sweden‡Southeastern Sweden‡
Origin of referentsPopulation basedPopulation based
No. included (n)Cases ×4Cases ×2
Age at enrolment, mean (years)4750
Age at participation§, mean (years)4758