Table 2 Age- and sex-adjusted mean values (x̄) of anti-CCP antibodies and of antibody ratios to citrulline-/arginine-containing (C/A) (I) and (II) C-telopeptides by sex and tertiles of age and each antibody among future cases of rheumatoid arthritis and their controls

Variable	Category tertile*	Cases of RA						Controls			Controls
		Anti-CCP (unit)			C/A (I) ratio			C/A (II) ratio			Anti-CCP (unit)			C/A (I) ratio			C/A (II) ratio
		x̄	r	p	x̄	r	p	x̄	r	p	x̄	r	p	x̄	r	p	x̄	r	p
Sex†	Men	311.7			2.8			1.3			16.2			0.91			0.93
Sex†	Women	108.9	0.23	0.01	1.2	0.19	0.04	1.4	0.01	0.88	16.1	0.02	0.66	0.90	0.02	0.66	0.90	0.10	0.05
Age‡ (years)	<41	139.8			1.0			1.0			16.3			0.91			0.89
	41 to 50	183.3	0.06	0.83	2.6	0.20	0.11	2.2	0.20	0.008	16.0		0.82	0.91	0.06	0.53	0.91	0.14	0.03
	⩾51	195.0			1.3			1.0			16.1			0.89			0.93
Anti-CCP (unit)	Lower				1.3			1.1						0.88			0.92
	Medium				1.1	0.11	0.49	0.9	0.12	0.40				0.92	0.14	0.04	0.93	0.13	0.04
	Higher				2.0			1.7						0.90			0.89
C/A (I) ratio	Lower	99.4						1.0			16.0						0.92
	Medium	39.5	0.29	0.01				0.8	0.23	0.06	16.7	0.08	0.32				0.90	0.07	0.47
	Higher	312.6						2.2			16.0						0.91
C/A (II) ratio	Lower	82.4			1.1						16.7			0.91
	Medium	164.7	0.15	0.25	0.8	0.22	0.07				16.1	0.12	0.09	0.89	0.06	0.52
	Higher	236.8			2.5						15.6			0.90

*The tertiles are based on the distributions among controls; †adjusted for age only; ‡adjusted for sex only.
r = partial correlation coefficient based on continuous variables and p = statistical significance for its difference from zero.