Table 2. Crude and covariate-adjusted hazard ratios (HRs) for rheumatoid arthritis among the sampled subjects during the 5-year follow-up period.

Development of rheumatoid arthritis	Total sample (N = 17,176)		Subjects who underwent an appendectomy (N = 4,294)		Comparison subjects (N = 12,882)
	No.	%	No.	%	No.		%
Five-year follow-up period
Yes	93	0.54	33	0.77	60		0.47
Crude HR (95% CI)	-		1.66* (1.08~2.54)			1.00
Adjusted a HR (95% CI)	-		1.61* (1.05~2.48)			1.00

Notes: CI, confidence interval. The HR was calculated by a stratified Cox proportional hazard regression which was stratified by sex, age group, and the year of the index date.

^a Adjustments were made for subjects’ monthly income and geographic region.

* p<0.05.