Table 3.

Study population characteristics compared by social class grouping^*

Characteristics	No.	I, II (n = 385)	IIINM (n = 359)	IIIM (n = 279)	IV, V (n = 370)	P
Age at symptom onset, years	1,393	54 (44–67)	56 (45–68)	55 (42–66)	55 (43–66)	0.580
Women, no. (%)	1,393	250 (65)	301 (84)	102 (37)	274 (74)	< 0.001†
Symptom duration at registration, months	1,393	5 (2–13)	5 (2–13)	5 (2–14)	6 (2–12)	0.861
Current smoker, no. (%)	1,334	80 (22)	66 (19)	78 (29)	104 (29)	0.003†
Baseline HAQ score	1,393	0.75 (0.25–1.25)	0.88 (0.25–1.50)	0.75 (0.25–1.50)	0.88 (0.38–1.50)	0.814
Year 3 HAQ score	1,393	0.63 (0.13–1.38)	0.88 (0.25–1.50)	0.63 (0.00–1.25)	0.88 (0.25–1.75)	0.290
Change in HAQ from baseline to year 3, mean ± SD	1,393	−0.02 ± 0.64	−0.001 ± 0.65	−0.08 ± 0.67	0.03 ± 0.71	0.202‡
Baseline swollen and tender joint count	1,393	2 (0–5)	2 (0–6)	2 (0–7)	2 (0–7)	0.064§
Year 3 swollen and tender joint count	1,314	0 (0–2)	0 (0–3)	0 (0–2)	0 (0–3)	0.069§
Change in swollen and tender joint count from baseline to year 3, mean ± SD	1,314	−1.4 ± 6.1	−2.5 ± 7.0	−3.1 ± 6.6	−2.5 ± 8.0	0.017
Baseline RF positivity (titer ≥1:80), no. (%)	1,247	101 (29)	109 (34)	77 (31)	98 (30)	0.531†
Year 3 RF positivity (titer ≥1:80), no. (%)	1,284	142 (40)	153 (46)	107 (41)	138 (41)	0.334†
DAS28 score at baseline	1,069	3.7 (2.8–4.5)	3.8 (2.8–4.8)	3.9 (2.8–5.1)	3.8 (2.8–4.9)	0.331
Satisfy ACR criteria at baseline, no. (%)	1,393	168 (44)	169 (47)	128 (46)	168 (45)	0.822†
Satisfy ACR criteria by year 3, no. (%)	1,393	265 (69)	245 (68)	193 (69)	261 (71)	0.921†

^*Values are the median (interquartile range) and the model used is median regression, unless otherwise indicated. Scale is I, II = highest social class and IV, V = lowest social class. IIINM = social class III nonmanual; IIIM = social class III manual; HAQ = Health Assessment Questionnaire; RF = rheumatoid factor; DAS28 = Disease Activity Score in 28 joints; ACR = American College of Rheumatology.

^†Logistic regression.

^‡Linear regression.

^§Negative binomial regression.