Table 3

Proportion of cases attributable to smoking EF by SE alleles, regarding ACPA-positive RA, ACPA-negative RA and total RA

ACPA-positive RA
	No SE		Heterozygotic SE (SSE)		Homozygotic SE (DSE)
Smoking dose	No of cases/controls	EF%^* (95% CI)	No of cases/controls	EF%^* (95% CI)	No of cases/controls	EF%^* (95% CI)
Non-smoker	38/154	Ref^†	107/150	Ref^†	62/43	Ref^†
Ever smoked	73/259	11 (−19 to 33)	275/223	29 (14 to 43)	180/42	55 (39 to 67)
ACPA-negative RA
	No SE		Heterozygotic SE (SSE)		Homozygotic SE (DSE)
Smoking dose	No of cases/controls	EF%^* (95% CI)	No of cases/controls	EF%^* (95% CI)	No of cases/controls	EF%^* (95% CI)
Non-smoker	90/154	Ref^†	87/150	Ref^†	25/43	Ref^†
Ever smoked	115/259	−14 (−39 to 7)	124/223	0 (−22 to 19)	28/42	7 (−25 to 38)
Total RA
	No SE		Heterozygotic SE (SSE)		Homozygotic SE (DSE)
Smoking dose	No of cases/controls	EF%^* (95% CI)	No of cases/controls	EF%^* (95% CI)	No of cases/controls	EF%^* (95% CI)
Non-smoker	128/154	Ref^†	194/150	Ref^†	87/43	Ref^†
Ever smoked	188/259	−7 (−28 to 11)	399/223	19 (1 to 34)	208/42	47 (30 to 60)

↵* Excess fraction in per cent (EF%) with corresponding 95% CI.
↵† Reference category.
The EF% attributable to smoking and risk of anticitrullinated protein/peptide antibody (ACPA)-positive rheumatoid arthritis (RA) without consideration of shared epitope (SE) status is 35 (95% CI 25 to 45), ACPA-negative RA EF% is −5 (95% CI −21 to 10) and RA total EF% is 20 (95% CI 11 to 29).
DSE, double shared epitope; SSE, single shared epitope.