Extended report Norwich Health Authority, with notiﬁcation of cases through general practitioners or attendance at hospitals. Those who were subsequently diagnosed by a hospital consultant as hav- ing a condition other than RA, IP, psoriatic arthritis or postviral arthritis were excluded. Between 1990 and 1994, 1098 subjects were registered with NOAR who satisﬁed the above criteria. Fourteen subjects were excluded as they had begun DMARD or steroid treatment for another condition before the onset of IP symptoms, leaving 1084 subjects. Data collection Baseline Clinical and demographic data were collected by a research nurse by a structured interview and clinical examination shortly after registration (baseline) as outlined in table 1. Detailed information was collected on the use of DMARDs and steroids (DMARD/S) and hospital attendance for patient with IP. Each subject com- pleted the Health Assessment Questionnaire (HAQ), modiﬁed for use in British patients.14 A blood sample was taken for rheumatoid factor (RF), anti- cyclic citrullinated peptide antibody and C-reactive protein (CRP) testing. The Disease Activity Score (DAS28) was calcu- lated from the 28 tender joint count, 28 swollen joint count and CRP (http://www.das-score.nl/www.das-score.nl/index.html, accessed 14 January 2010). Human leucocyte antigen (HLA) genotyping was performed as described previously.15 Subtyping at the HLA-DRB1 locus was performed to identify the presence of the shared epitope. Follow-up Annual assessments were carried out for 3 years, then at ﬁfth, sev- enth and tenth years. Dates of starting and stopping any DMARD treatment since the last assessment were recorded as well as the rea- sons for stopping (eg, inefﬁcacy, adverse events). Blood was taken for RF testing at the ﬁrst and second annual assessment if the subject had been RF negative previously. A blood sample was taken from all subjects at the ﬁfth and tenth assessments for RF and CRP testing. The American College of Rheumatology (ACR) 1987 classiﬁcation criteria for RA were applied both cross-sectionally at baseline and cumulatively at each assessment, as described previously.16 Patients attended for x-ray examinations of their hands and feet at the ﬁrst and/or second assessment, if they had already satisﬁed the ACR criteria for RA or if the presence of erosions would lead to the patient satisfying them. All patients were invited to have x-ray examinations at the ﬁfth assessment and only those who were erosive at the ﬁfth were invited to the tenth assessment. Radiographs were scored using the Larsen method17 by two rheumatologists, and major disagreements were arbitrated by a third.18 Patients completed the Medical Table 1 Variables used in the marginal structural weight models Variable Demographics Age at symptom onset and at each assessment Gender Months from symptom onset at baseline and at each assessment Smoking status at each assessment Serological and genetic Anti-CCP status at baseline (Axis-Shield DIASTAT kit) CRP category at baseline and assessment (end point immunoturbidimetric agglutination) RF status at baseline and by assessment (latex agglutination) Number of copies of the SE Homozygous for SE Disease activity and severity DAS28 score at baseline and assessment ACR criteria for RA cross-sectional at baseline and cumulative at assessment Number of swollen, tender and (both tender and swollen) joints at baseline and assessment Presence of nodules at baseline and assessment HAQ group at baseline and assessment Presence of erosions by assessment Larsen score by assessment Physical Component Score (PCS) of SF36 Mental Component Score (MCS) of SF36 Diagnosed with any of 14 deﬁned comorbidities by assessment Treatment and hospital attendance Attended/referred to hospital since last assessment Treated with SSZ, MTX, other DMARDs and steroids at baseline and by assessment Ceased treatment since last assessment or by assessment due to inefﬁcacy or adverse event Remission by baseline and assessment Variable type Decades Male/Female Tertiles by assessment <5 U/ml/≥5 U/ml ≤ 10 mg/l/>10 mg/l <1:40/ ≥1:40 0/1/2 No/Yes Not met/Met Tertiles by assessment No/Yes <1/≥1 to <2/≥2 No/Yes Tertiles by assessment No/Yes No/Yes No/Yes No/Yes No/Yes Never smoked/Stopped ≥ 10 years before assessment/ Stopped <10 years before assessment/Current smoker ACR, American College of Rheumatology; anti-CCP, anti-cyclic citrullinated peptide; CRP, C-reactive protein; DAS28, 28 joint count Disease Activity Score; DMARDs, disease-modifying antirheumatic drugs; HAQ, Health Assessment Questionnaire; MCS, Mental Component Score; MTX, methotrexate; PCS, Physical Component Score; RA, rheumatoid arthritis; RF, rheumatoid factor; SE, shared epitope; SSZ, sulfasalazine. 690 Ann Rheum Dis 2010;69:689–695. doi:10.1136/ard.2009.108639