Table 4. Incidence density rates and hazard ratio for chronic fatigue syndrome risk stratified by the severity of dry eye syndrome.

Average frequency for medical visit, per years	N	Event	Person-years	IR	Adjusted HR (95% CI)
No DES cohort	3536	54	17986.70	3.00	1.00
DES cohort
<1	555	7	2975.44	2.35	0.63 (0.28–1.39)
1–2	244	13	1148.86	11.32	3.01 (1.61–5.64)***
≥3	85	8	365.57	21.88	4.88 (2.26–10.58)***
p for trend					<0.001

Abbreviation: IR, incidence density rates, per 1,000 person-years; HR, hazard ratio; CI, confidence interval; DES, dry eye syndrome.

Adjusted HR: adjusted for age, gender, and comorbidity in Cox proportional hazards regression.

^*** p < 0.001.